Posted On: Thu, Dec-25-2008
Reviewer: OklahomaWolf
Product: Seasonic M12D 850W
Product Link:
Supplied By: Seasonic
Price: $299 @ Newegg


A little while back, I reviewed Antec's Signature series 850W power supply. Toward the end of that review, I threw down a challenge: any company who though they could do better than that unit should give it a shot and send me the resulting power supply.

While I'm still waiting for responses from the likes of Zippy and PC Power and Cooling, Seasonic came through for me. I'm looking at the latest and greatest from them today in the M12D 850W unit, a beast of a power supply promising 70A of combined 12V capacity and bringing 80 Plus Silver certification with it. Let's see if it will do better than the Bronze certified Signature, shall we?

Page 1 -

Recently, a lot of fantastic units have been coming out around the 850W mark. Case in point, the Antec Signature 850W and the Corsair TX850 I reviewed last week. Now, Seasonic has decided they want into this market, and have sent me the brand new M12D 850W as proof of how serious they are about it. Let's get started with a few of the usual box pictures, and then we'll let my SM-268 load tester find out how serious Seasonic really is.

Going by the box picture above, I'd have to say things are looking good already, for it bears a prominent 80 Plus silver logo on the front. Also present are an nVidia SLI ready logo, a Sanyo Denki logo with a picture of a fan on it, and a weird little diagram that seems to suggest that the unit uses DC to DC conversion for coming up with the 3.3V and 5V rails.

"The Ultimate Modular Gaming Power Supply," crows the box in proud white lettering. You let me be the judge of that, Mr. M12D. Look over there... see that? See my Antec SG-850 frowning at you? It doesn't think you can do it. But, I'm sure going to let you try... after all, I did throw down a challenge to see if there was any company out there who could do better than that unit.

Our next stop will be the back of the box, where all the bragging points are, as well as a load table. The above picture is too small to make anything out, so here you go:

  • Super High Efficiency (up to 90%) - Green solution for lowering energy consumption, noise & heat.
    90% is very impressive, if this claim holds true.
  • DC to DC Converter Design - Superior dynamic response & greater system stability.
    Nothing new here... a lot of high end units are using the VRM approach to derive 3.3V and 5V from the 12V supply.
  • Practical Dual +12V Rails - Ample +12V output with OCP for extreme utilization.
  • Tight Voltage Regulation - Improved load regulation to reduce voltage variations.
    We'll let the SunMoon be the judge of that on the next page.
  • Highly Reliable 105°C Japanese Brand Capacitors - Exceptionally reliable components extend product life.
  • Solid Caps on 12Vs for Extreme Stress Operating Conditions - Enhanced stability at severe operating conditions.
  • Active Power Factor Correction (99% PF) - Reduces line loss & power distortion.
    Again, nothing new - all high end units these days have APFC. This is good. Unless you happen to be a guitarist in a rock band, that is - then you might want that power distortion.
  • Dual Sided PCB Layout - Better utilization of PCB space to enhance quality and performance.
    I'm not sure an advanced high power unit like this could be designed with a single layer PCB.
  • Detachable Modular Cables - Flexible cable solution to reduce clutter.
  • San Ace Silent Fan (Sanyo Denki) - Premium quality fan for silent operation.
  • Smart & Silent Fan Control (S2FC) - Smart thermal control to balance between noise & cooling.
  • Ultra Ventilation (Honey Comb Structure) - Minimizes airflow resistance for maximum cooling.
    I'm starting to think Seasonic uses everything as a marketing point. Fan grille! Power switch! Power cord! Advanced thermal dissipation device (fan)! Oh wait, they actually do brag about the fan... never mind.
  • Multi-GPU Technologies Supported - 6P and 8P PCI-E connectors to support all multi-GPU platforms.
    All, you say? Even three way SLI with 280's? Seems a bit unlikely... let's not get ahead of ourselves, here.
  • All-in-one DC Cabling Design - Supports PC, IPC, workstation, and server systems.
  • Universal AC Input - Plug & run safely anywhere in the world.
    Yay! Now I can move forward on my plans to build a rig at the summit of Mount Everest!
  • Patented Easy Swap Connector - Unplug the connectors easily, quickly, and safely.
  • 5 Year Warranty - Our commitment to superior quality.
    Five year warranties are good.

Just thought I would show you a quick shot of the bottom of the box, where the above listed bullet points are relisted in a half dozen more languages. Mmm... eggnog. The cup seems to be empty now. Here, look at this picture of the side of the box while I go get some more.

Ah, that's better. As you can see above, Seasonic wasn't quite done with their bragging points yet, for there are more of them here along with some fancy connector pictures and a diagram of the modular connector panel on the unit.

And on the opposite side, yet more bragging points are listed. Wow, they really do turn everything into a feature to brag about. Even if someone forgot to turn on their "advacned" spell checker.

Hey, how did my eggnog cup get empty again? There must be a hole in it. I'll go get more in a second, once you've had a chance to look at these two shots of the box opened up.

Ah, it looks like we get a nice carrying bag for the modular cables. Sweet. And now, to go get that eggnog. Be right back.

Ah, my taste buds love this time of year. Where was I? Oh yes, the above picture. As you can see, the M12D comes with lots of goodies. Modular cables, a manual, a little bag full of screws and a case badge, a thick 16AWG power cord, and that modular cable carrying case I mentioned a second ago.

The M12D, once you get it out of the bubble wrap, turns out to be housed in a nice matte black enclosure. I sure do love matte black, almost as much as this here eggnog. What? The cup's empty again! I think I'll go get the whole container. I hope this isn't the extra happy kind of eggnog... my head seems to be buzzing for some reason. No, wait, it's just a fly. I don't know where these bugs come from in the dead of winter... sorry, got off track there.

A view of the back shows something else I like to see - fully sleeved cables that don't stop short of the enclosure. Not only does this give the M12D a clean look, it keep the cables from chafing against the plastic grommet. I'll show you an up close look at the modular connector panel a bit later on this page. Meanwhile, here's the part of the label with the load table.

Well then... somebody decided to put some serious output on the 12V side of this unit, it seems, for the 12V rails get 840W combined to themselves. That's identical to the Corsair TX850 from last week, and 5A more than the Signature. Impressive, yes, but since this is only 10W away from the maximum spec on the unit I'm not sure there would be many occasions you'd be able to get the whole 70A from this thing.

Seasonic SS-850EM +3.3V +5V +12V1 +12V2 -12V +5VSB
24A 30A 40A 40A 0.8A 3A
Max Power 150W 840W 9.6W 15W

A shot of the connector side of the hardwired cables shows the well done sleeving in its entirety. It leaves, in my opinion, just the right amount of unsleeved wires at the end to be serviceable, and yet it doesn't leave so much as to leave things open for tangling.

I promised an up close shot of the modular panel, and here it is. The rail distribution is a bit funky on this, but Seasonic was kind enough to enlighten me. From left to right in the above picture, the connectors are: 12V1, 12V1, 12V2, 12V2, 12V1, 12V2. This means that the PATA/SATA connectors are evenly divided between the two 12V rails, as are the PCI-E connectors. The hardwired cables are similarly divided - 12V2 for the EPS12V and ATX12V cables and one of the PCI-E cables, with everything else on 12V1.

Here are the codular mables... er, madular crabbles... uh... mod-u-lar ca-bles. Hmm, this eggnog seemsh t'be... loaded after all. Be'er go gessome coffee. Here's a lil... tableforya.

Type of connector: Seasonic
ATX connector (530mm) 20+4 pin
8-pin EPS12V connector (530mm) 1
4-pin ATX12V connector (530mm) 1
SATA (330mm+150mm+150mm) 3
2 x 4 PCIe (590mm) 2*
Modular Cables
5.25" Drive (550mm+150mm+150mm) 3
5.25" Drive (450mm+150mm+150mm) 3
5.25" Drive (350mm+150mm) 2
3.5" Drive connectors (+150mm) 1**
SATA (550mm+150mm+150mm) 3
SATA (450mm+150mm+150mm) 3
SATA (350mm+150mm) 2
2 x 4 PCIe (550mm) 2*
Unit Dimensions(L x W x H)
160mm x 150mm x 86mm

*connectors are 6+2 pin modular type
**5.25" Molex to 3.5" drive connector adaptor

Page 2 -

Now that the deleterious effects of yonder spiked eggnog have worn off some, I do believe I'm ready to begin the load testing on the M12D. As usual, my instrument of PSU torture will be the good old SunMoon SM-268 automated test environment.

For those of you new to this, the SM-268 has the ability to precisely load a computer PSU any way I wish to load it, with units up to about 1100W in size. You can program in a set of five loads into the preset buttons on the front, or override them and manually configure the load any way you want.

I'm going to set up the 268's preset buttons for a simple, balanced, five stage progressive load test. It will start out at 20% of full rated power, at room temperature, and proceed up to full rated power, or 850W in the case of the M12D. Loads are chosen based on the combined ratings from the label to make sure no one rail gets overloaded. Once the five stage progressive test is done, I'll do two crossload tests to see how the unit likes a curve ball. First, a heavy 3.3V/5V test will see how stable the unit can keep itself, and then a heavy 12V test to see how this unit would behave if all of a sudden a couple of 4870 x2's came online at full blast.

But that's just the first test. The second test, which measures power-on overshoot transients, is a look at how the unit's 5VSB and 12V rails behave when the unit is first powered up. This test looks for spikes that go out of spec, and negative voltages. Finding either one is bad.

Finally, the third test will see the unit locked in a box with the entire heat output of the SM-268 channeled into it. Then, the progressive and crossload tests will be repeated. This will show us what effect heat has on the poor wee thing.

Throughout load testing, I'll be using a very accurate (not to mention expensive) Brand 4-1850 to give me some at the wall power draw readings. This will give me a way to show you the efficiency, and see whether or not that 90% claim on the box was accurate.

Results from Seasonic SS-850EM COLD load tests
Test # +3.3V +5V +12V1 +12V2 DC Watts/
AC Watts
Eff. Intake/
Simulated system load tests
3A 3A 6A 6A 192W/
87.9% 21°C/
3.37V 5.02V 12.30V 12.30V
5A 5A 12A 12A 353W/
87.2% 22°C/
3.34V 5.00V 12.24V 12.28V
7A 8A 18A 18A 523W/
87.2% 23°C/
3.31V 4.96V 12.20V 12.26V
9A 10A 24A 24A 686W/
85.6% 23°C/
3.28V 4.93V 12.16V 12.24V
12A 13A 30A 30A 857W/
84.6% 23°C/
3.24V 4.88V 12.10V 12.22V
18A 18A 1A 1A 193W/
81.4% 23°C/
3.32V 4.93V 12.14V 12.12V
1A 1A 35A 30A 813W/
85.3% 23°C/
3.31V 4.96V 12.14V 12.24V

Wow, this must be some good eggnog. It almost looks like no test goes below 80% up there, or something. Wait a minute... those are the real numbers! This is fantastic! I knew this unit was 80 Plus certified, and thus guaranteed to do 85-87-85% efficiency, but I didn't know it was going to keep above 80% in the heavy 3.3V/5V crossload test! This unusual, to say the least.

The news isn't all good for efficiency, however, as the test five numbers see it drop below 85%, but we can excuse that this time. Why? Because for one thing, it was putting out more than 850W at the time. In fact, it was putting out 7 watts more than full rated power. For another thing, if you round off the number I got, you get 85% anyway. Woohoo!

Moving on to the voltage readings, take a look at that... rock solid 12V readings. The worst drop is 0.18V - that's excellent. The 3.3V and 5V rail could use a little work though, it looks like, for this isn't quite the tightest regulation I've ever seen. Not too big a deal though, as these rails are afterthoughts in a modern rig.

Overshoot Transient Testing - Seasonic SS-850EM
VSB to Full 12V
Off to Full 12V

Moving on to the overshoot transient test, this happens in three stages. First, I have the scope watch 5VSB when I flip the main switch on. Then, I have it watch the 12V1 rail when I first power up the unit to full load from standby, and then once more by using the power switch. Any spikes show up in the above scope shots. The ATX spec calls for these spikes to be kept below 10% over mean value.

And there's very good news here, for the spikes are well in spec and there are no negative spikes present. These readings are so good, in fact, that even the NorthQ Giant Reactor is hard pressed to compete.

Results from Seasonic SS-850EM HOT load tests
Test # +3.3V +5V +12V1 +12V2 DC Watts/
AC Watts
Eff. Intake/
Simulated system load tests
3A 3A 6A 6A 192W/
86.9% 28°C/
3.37V 5.03V 12.30V 12.30V
5A 5A 12A 12A 355W/
87.9% 31°C/
3.34V 5.00V 12.24V 12.28V
7A 8A 18A 18A 523W/
87.3% 34°C/
3.32V 4.96V 12.23V 12.25V
9A 10A 24A 24A 684W/
85.8% 38°C/
3.29V 4.94V 12.16V 12.14V
12A 13A 30A 30A 852W/
84.3% 43°C/
3.25V 4.90V 12.10V 12.07V
18A 18A 1A 1A 189W/
81.1% 35°C/
3.31V 4.84V 12.29V 12.29V
1A 1A 35A 30A 816W/
85.2% 41°C/
3.31V 4.96V 12.12V 12.14V

Moving on to the hot box, it becomes apparent that the unit doesn't seem to mind the heat much. Efficiency is down on some tests, but not down by a lot. If anything, voltage regulation has gotten a bit tighter, with the 3.3V not budging an inch between tests CL1 and CL2. And the 12V rails are still rock solid. Very good.

What was really amazing about all this was the lack of fan noise. I just couldn't hear it in any test, and that's a very good thing considering I saw temperatures exceeding 40 degrees. Let's take a look at the scope shots, obtained by my trusty USB Instruments Stingray DS1M12.

Oscilloscope Results - Seasonic SS-850EM
Test #

There's some interesting stuff up there. While nothing at all is out of spec, and most of the time the unit never even comes close to spec, it looks like this unit has gotten bitten with the boogie woogie bug, for there is some low frequency ripple present around 120Hz. Otherwise, noise suppression is nothing short of amazing, with no one rail getting far above 10mV. Ripple suppression, on the other hand, is not so good with the 12V rails hitting close to 40mV. But complaining about that 40mV is a bit like complaining because your brand new Mercedes isn't a Bentley. It's still excellent performance.

Page 3 -

And now for my favorite part - the "ripping the expensive brand new PSU" apart part. It's partly cloudy here as I partly listen to the Partland Brothers' songs that I'm partial to.

Just like the box said, the fan is a Sanyo Denki 9S1212H403.

Some of the transient filter can be found on this PCB mounted to the back of the AC receptacle.

And the rest of it can be found in the bottom center of this picture, in the corner of the PCB, near that little black relay.

Going by these markings, we can see that this PCB is shared by the 750W and 850W versions.

Here's the modular connector PCB, which helpfully lists the exact rail distribution beneath each connector and also supplies several extra capacitors for filtering. All capacitors are Nippon Chemi-Con by the way. You know, maybe I just wasn't looking hard enough, but I didn't see any solid polymer caps on the 12V rails like the box said there were.

This would be a good time to mention that the two 12V rails share a single source. They are split using overcurrent protection, just like 99% of the other multirail units out there.

If you look real close, up in the top left corner is the protection IC - a PS223. Soldering in general is leaps and bounds better than the soldering I saw in the Antec Neopower Blue, which is also Seasonic based, but still not quite perfect - there were a few spots where there was too much solder and other isolated blips.

In fact, I had two of these units because my first one decided to play out the whole Easter story in miniature. Yes, friends, it died in the hot box, went through the autopsy picture phase, got put back together, and still didn't work (standby only). Then, magically, a few days later it came back to life, going on to complete another full set of tests. What's even more astonishing is, it passed the hot box tests the second time around.

You know what that tells me? Solder bridge. I must have cleared one out without realizing it. And now, back to our irregularly scheduled pictures.

See that little card sticking up down in the bottom left there behind the relay? That houses the combination PWM/PFC controller, which is a CM6802BHG. This is a chip I've never seen before, and it looks like Google hasn't seen it before either at this point in time.

On the left you can see the big vertical card that is the 3.3V/5V VRM. This is where I saw the only polymer capacitors in the unit. Those two reddish coils on the right? Those are for the PFC circuit. The three coils above them are for the AC transient filter. Two ginormous Chemi-Con capacitors in the center do the main filtering duties.

A closer look at the VRM. Yep, those solid caps are still Chemi-Con. Seasonic was kind enough to send me a complete spare VRM, which I took apart to ID the working components. Those include two APW7073A buck controllers, and a total of seven APM2556N MOSFET's; three for the 3.3V rail, four for the 5V rail.

Above is the primary side heatsink. This carries a total of four FDP18N50's plus two diodes for the PFC, and two GR125P's in double forward for the main switchers.

The 12V secondary parts turned out to be eight 30A50CT Schottky's in parallel.

Finally, the two bridge rectifiers get their own heatsink. Two GBU806's in parallel.

Page 4 -

Performance (40% of the final score) - I have to admit, this unit is very impressive. Absolutely astounding efficiency combined with some very stable voltage regulation is a real tough combo to beat already. Adding in that amazing ripple and noise suppression, it's tough to find stuff to hate about it. But find stuff I did, for that soldering job needs to be cleaned up. And guess what - Seasonic's already working on that. But all the same, I need to pull half a point for that. 9.5.

Functionality (20% of the final score) - the story even better for this part of the score, because... well, the "M" in the M12D stands for Mary. As in, a certain nanny famously played by Julie Andrews. As in, practically perfect in every way. First there's a fan that can't be heard over the duration of my load testing process. Then, you have the fact that they not only threw in a bunch of perfectly sleeved modular cables, the SATA and PATA cables are of different lengths so you can plan out cable management better. Finally, you have four PCI-E cables, all of which have 6+2 pin modular connectors. I mean, the only way things could get better would be to add another couple hundred watts and a couple more PCI-E connectors. 10.

Value (30% of the final score) - Newegg is listing the M12D right now for $299.99. Ow, ow, ow. This puts it into solid competition with the Antec Signature 850W. I hate to say it, but... it's good, but not quite that good. Not with the soldering not quite as good, anyway. 8.

Aesthetics (10% of the final score) - nothing at all to complain about here. It looks awesome, the sleeving is well done, and the whole thing just screams quality while that SanAce fan spins slowly around and doesn't scream anything. A second 10 goes here.









Total Score



The Seasonic M12D came promising the moon, the stars, and even the Starship Enterprise with which to explore them by, and for the most part the voyage is a successful one. Excellent stability combined with extremely high efficiency on top of outstanding ripple and noise suppression makes this unit one to watch.

The Good:

  • extremely efficient
  • good voltage regulation
  • very quiet fan
  • nice sleeving job

The Bad:

  • low frequency boogie woogie ripple on the 12V rails (if you can really call 40mV bad)

The Mediocre:

  •  I'm out of eggnog... and coffee

This review was provided by : JonnyGURU

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