Reviews - Mushkin HP-550 550W
Sample Provided by: Mushkin (By jonny on Mon, Jul-24-2006)

Page 1 -

Mushkin Enhanced, a brand synonymous with high-end RAM, had recently announced the addition of the HP-550 Power Supply to its new power supply product lineup last month.

Mushkin launched the XP-650 in May of this year. That power supply is fairly expensive, and supposedly has the performance to match it's price (please note that I've yet to test one myself.) But for a moment it would seem that Mushkin had forgotten the mainstream user by not offering something a little more affordable.

Mushkin decided to swing to the other side of the power supply price-point spectrum, still offering modular connectors and "Rail Fusion", but in a unit that could sell for under $100.

The shiny finish is the first sign that tells us that this power supply, like their higher end unit, is made by Topower. The HP-550 also features EMI/RF filters on the "snake-skinned" PCI-e cables. Another Topower signature item.

The box is very... white? It's sort of art deco in a Miami Vice Don Johnson kind of way. Not that a box has anything to do with how a power supply performs, but I couldn't help to notice that there were no pictures of the power supply showing the modular interface or any of it's cables.

All of our modular cables are stored in a separate box. The power supply is wrapped in bubble wrap and sitting loose at the bottom of the box.

All of the cables are nicely sleeved in a nice, tight, black nylon sleeving.

While we have this separate box busted out and open for a photo, let's go ahead and do our customary cable count...

Type of connector: Mushkin HP-550
ATX connector 20+4
2 x 2 12V connectors 1
2 x 3 PCIe 2
8-pin Xeon/EPS connector 1*
6-pin Xeon/AUX connector 0
5.25" Drive connectors


3.5" Drive connectors 1
SATA Drive power connectors 4
Fan only connectors (thermostatically controlled 12V only) 0

* Two four pin connectors combine to create one 8-pin EPS+12V connector.

Now let's take a look at the exterior of this bad boy. Particularly the side that's never shown in a picture on the box.

Here we can see that our main ATX cable is fixed and we have two separate 4-pin connectors that can be snapped together to make a single 8-pin connector for use in EPS+12V boards.

There's also a ground wire with a ring terminal on the end. This is a great idea as a lot of cases out there don't offer very good grounding.

The box may be plain looking, but it does have good information. For example; the entire PSU DC output specification table is laid out on one side of the box. Ironically, the specs on the box are easier to read, because of the traditional table format, than the specs on the PSU label (shown below.)

This power supply has a pair of +12V rails, each set to do 20A. The combined 12V capability is 336W, or 28A.

What this typically means is that you can put as much as 20A on each 12V rail, but never more than a total of 28A on both at the same time. But the Mushkin HP-550 has what's called "Rail Fusion." "Rail Fusion" is what Topower calls it when a PSU's rails can be combined to create one big 12V rail.

So obviously the "20A" rating on each rail means nothing. Why even bother with two 12V rails? Well, even though this PSU can not be considered ATX12V compliant since you have rails that are capable of more than 240VA, the rails are capable of isolating EMI from one another. So you do get one of the positive features of split 12V rails while not having to deal with the negative feature of "running out of available power."

Mushkin HP-550
+3.3V +5V +12V1 +12V2 -12V -5V +5VSB
24A 30A 20A 20A 0.8A 0.5A 2.5A
Max Combined Watts 220W 336W 9.6W 2.5W 12.5W
530W 25W

Supposedly, I can put 14A on each 12V rail at the same time for a total of 28A. And because of "Rail Fusion" I should be able to put 28A on one 12V rail as long as there's nothing on the other.

With a sticker that says "Rail Fusion Active" one would think this LED lit up whenever a 12V rail exceeded it's set limit, causing "Rail Fusion" to kick in, negating the separate rails. One would think.

When the power supply is plugged in and flipped "on" (standby) the green light on the back of the PSU tells us the unit is live. But once the PSU is turned on, the green LED on the back cuts out and the green LED on the fan kicks on. But does the LED tell us when "Rail Fusion" is active?

Since we now know what the HP-550 should be capable of and we have a basic understanding of how "Rail Fusion" should work, it's time to set up the load tester. If you're not familiar with my testing methodology, you need to check this out.

Because of "Rail Fusion" I've added a test where I've intentionally overloaded one of the rails while having no load on the other.

To break it down: On Tests 1 through 4, I've gradually loaded all of the rails up with fairly balanced increments until the 12V rails met the combined output capability of 28A (14A on each 12V rail.)

For Test 5, 12V2 is pushed to the 20A limit while the 12V1 is reduced to 8A. This is actually quite a realistic load since the 12V1 only powers the CPU and it's not likely you'll push a CPU to need more than 8A.

Test 6 is simply a test of "Rail Fusion" where I put all of the 12V load on one rail while the other has no load at all.

Results from Mushkin HP-550 COLD load tests
+3.3V +5V +12V1 +12V2 Watts Efficiency P.F. Intake Exhaust
Simulated system load tests
2A 4A 3A 3A 114.3W 76% .65 28°C 28°C
3.37V 5.11V 11.98V 11.98V
5A 8A 7A 7A
239.8W 79% .71 28°C 29°C
3.35V 5.10V 11.91V 11.94V
7A 12A 10A 10A
336.8W 78% .75 28°C 30°C
3.34V 5.08V 11.84V 11.88V
10A 16A 14A 14A
458.8W 76% .76 29°C 32°C
3.32V 5.05V 11.73V 11.79V
12A 20A 8A 20A
487.4W 74% .76 30°C 35°C
3.30V 5.01V 11.88V 11.84V
12A 20A 0A 27A 474W 75% .76 30°C 36°C
3.29V 5.00V 11.96V 11.80V

Note the load on 12V2 during test 6 is only 27A. Anything higher than this would trip the power supply. Strange really, since I could put 14A load on each 12V rail for 28A, and I could put 8A on one rail and 20A on the other for a total of 28A, but when only one rail is loaded I can only do 27A.

I want to assure readers that the drop in voltage between test five and six should not concern anyone. During test six, I'm merely testing "Rail Fusion." The bulk of the voltage drop can be primarily contributed to the resistance caused by the additional load on a single connector.

The voltage on the 12V rail dropped only .14. Not bad. Even the 3.3V and 5V looked respectable.

As for noise, By test three, the fan was noticeably audible.

Now for the bad news... The efficiency was mediocre and there's no power factor correction. So what could have potentially been a performance score of 9 is now a 7.

Let's see how it does in the hot box...

Results from Mushkin HP-550 HOT load tests
+3.3V +5V +12V1 +12V2 Watts Efficiency P.F. Intake Exhaust
Simulated system load tests
2A 4A 3A 3A 114.2W 75% .64 32°C 36°C
3.36V 5.10V 11.95V 11.96V
5A 8A 7A 7A
238.8W 79% .71 35°C 42°C
3.34V 5.08V 11.86V 11.88V
7A 12A 10A 10A
335.3W 78% .75 37°C 46°C
3.33V 5.05V 11.77V 11.81V
10A 16A 14A 14A
457W 75% .76 37°C 50°C
3.30V 5.03V 11.68V 11.74V
12A 20A 8A 20A
485.5W 74% .76 38°C 52°C
3.29V 5.00V 11.83V 11.80V
12A 20A 0A 27A 473W 74% .76 39°C 53°C
3.28V 4.99V 11.93V 11.77V

From the moment the 30 minute burn-in was over and I picked up the pen to write down the results of test 1, the fan was audible. It never got really loud, but you could definitely isolate that the noise coming from inside the case was a PSU fan.

When comparing the cold load to the same hot load, we see that there's as much as a .06V drop during test two and .07 during test three. The performance score just dropped to 6.

Just when you thought it could get worse... the crossload tests cometh! With a 3A load on the 3.3V rail and a 4A load on the 5V rail and 14A on each 12V rail (all within specification) the 12V dropped to 11.24V! It took taking the 3.3V up to 5A and the 5V up to 8A to get the 12V rail back up to 11.40V.

Let's take a break from the torture and do the autopsy. Then we'll return to the load tester for the screenshots of the oscilloscope readings of the rails.

If you couldn't tell from the cables, the modular connectors or the finish of the unit, the insides are a dead giveaway that this Mushkin HP-550 is in fact built by Topower.

Capacitors were all "Asia X" brand. A brand I've never seen or heard of before now.

The back of the modular interface (below) looked interesting. Almost over complicated and a bit sloppy.

Now it's time to get back to the torturing... Below are the screenshots from the oscilloscope software. The output is measured at the end of the connector, by the load tester, and reported by my USB-Instruments Stingray.

You might find that most power supply specs will document that their PSU's as having ripple "< 100mV at full load" (.1V = 100mV), "<120mV at full load," etc. But some reviews out there are only reporting power supplies as having 40mV or 50mV of ripple under full load. That's because they're measuring ripple at the PWM. Now, I applaude ANY reviewer that's measuring any ripple at all, but to measure ripple at the PWM leaves out a lot of variables that can affect ripple at the end of the connector where your peripherals are plugged in. Factories measure ripple at the connector. Not at the PWM, which is why their numbers are always high. They're not just being conservative or having low expectations. All ATE equipment have Waveform Monitor outputs, so it's quite easy to get an accurate reading with a scope.

+3.3V +5V +12V1 +12V2
Test 1
Test 2
Test 3
Test 4
Test 5

Ripple seems to be almost 100mV on the 12V rail as early as Test 3. The somewhat random peaks and valleys exhibited during test 4 and 5 had me looking at the voltage output readings on the ATE. Sure enough, the voltages fluctuated so much, I could see it on the LED displays. I decided to take out the camera and shoot some video of the fluctuation.

To Mushkin's credit, the 3.3V was incredibly clean, even with a 12A load (equivalent to more than 6 sticks of RAM) the ripple was only 20mV. I changed the V/Div scale on my Oscope for the screenshot below so you can see how little ripple there was....

It's not industry secret that the majority of RAM returned to memory manufacturers were actually damaged by excessive fluctuations in voltage from the power supply. Mushkin, being a performance memory manufacturer, made sure that this would not be a problem by putting out a power supply that has almost no 3.3V ripple whatsoever.

Ok.. At this point, I'm sure you're quoting Steve Martin from the Pink Panther movie."Stop browbeating her! Can't you see she is sexy!"

Let's just score it...

Performance 5
Aesthetics 9.5
Value 6
Functionality 9
Total Score 6.5

Performance (weight of 40%) gets a 5. This power supply simply does little for me, outside of actually putting out 550W. Efficiency could be better, there's no power factor correction, and the performance decreased significantly when temperatures were increased. The crossload shows that a computer with a minimal load on the 3.3V and/or 5V rails is going to wreak havoc on the 12V rails and the excessive ripple on the 12V line makes me contemplate potential long term effects on peripherals.

Aesthetics (weight of 10%) is 9.5. The mirror finish looks great and the modular cables will make the inside of your PC look great too. The embossed "Mushkin" on the side of the housing is a nice touch too!

Value (weight of 30%) score is a 6. At $80, this is certainly an inexpensive unit. But I wouldn't trust it to a high end system, so I'm reluctant to call it a "good value"

For functionality (weight of 20%,) I'm giving this power supply a 9. It's modular and compact, making it very easy to use.

Overall, the Mushkin HP-550 manages to score a "6.5" Simply put, I don't recommend this product. But do not let this affect your impression of Mushkin power supplies overall. It needs to be said that the XP series is based on a completely different platform and is supposed to be at a completely different performance level as the HP series.


I think I said it best when I was laying down why the performance score was only a 6. Outside of actually putting out 550W, efficiency could be better, there's no power factor correction, and the performance decreased significantly when temperatures were increased. Ripple was high and crossloading potential is evident.

The power supply looks nice, the cables are nice and they're modular, but you can't bank everything on a power supply looking uber-smooth. This product has the Mushkin name on it, so people are going to have high expectations. I know I did.

The Good....

  • Modular
  • Nice cables
  • Nice miror-like finish

The Bad....

  • Voltages not very stable
  • Totally failed crossload tests

The Mediocre....

  • No PFC
  • Mediocre efficiency
  • Lots of ripple, even during middle-load testing


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