For testing, I plug the power supply into a Sun Moon SM-8800; a piece of test
equipment used to load up ATX power supplies. The load tester is programmed
to put 10 different loads on the PSU: 10%, 20%, 30%, 40%, 50%, 60%, 80%, 100%,
all of the load on just the +12V rail and the, finally, all of the load on
the +3.3V and +5V rails. The exhaust created by making this loads are vented
into the intake of the power supply. This is done so the power supply is operating
in an environment more similar to what it would be operating in when installed
in a PC chassis.

At each load, I measure the voltage of each rail, the wattage the PSU is putting
out, the wattage the PSU is pulling from the wall, the power factor, the temperature
of the air being sucked into the power supply and the exhaust air coming out
of the back of the power supply.

beQuiet! Dark
Power Pro P10-550W
HOT load tests

Test #

+3.3V

+5V

+12V

+5VSB

DC Watts/ AC Watts

Eff.

Power Factor

Intake/ Exhaust

Simulated system load tests

Test 0

0A

0A

0A

1.5A

7.5W/ 10.28W

73%

.51

24°C/ 24°C

4.93V

Test 1

1.3A

1.3A

3.0A

1.5A

111.1W/ 131.2W

84.7%

.98

24°C/ 27°C

3.34V

5.03V

12.15V

4.94V

Test 2

2.7A

2.7A

6.7A

1.5A

166.9W/ 190.8W

87.5%

.99

26°C/ 29°C

3.33V

5.03V

12.15V

4.94V

Test 3

4.0A

4.0A

10.4A

1.5A

166.9W/ 191W

87.4%

.99

27°C/ 30°C

3.33V

5.03V

12.15V

4.94V

Test 4

5.3A

5.3A

14.0A

1.5A

221.1W/ 250W

88.4%

.99

28°C/ 33°C

3.32V

5.02V

12.14V

4.94V

Test 5

6.6A

6.6A

17.7A

1.5A

276.7W/ 310.7W

89.1%

.99

29°C/ 34°C

3.31V

5.01V

12.14V

4.94V

Test 6

8.0A

8.0A

21.4A

1.5A

333.0W/ 373.5W

89.2%

.99

31°C/ 36°C

3.30V

5.00V

12.13V

4.94V

Test 7

10.6A

10.6A

28.7A

1.5A

442.3W/ 498.1W

88.8%

.99

33°C/ 40°C

3.28V

4.99V

12.12V

4.93V

Test 8

13.2A

13.2A

36.0A

1.5A

551.2W/ 624W

88.3%

.99

37°C/ 44°C

3.26V

4.97V

12.11V

4.93V

Test CL1

0A

0A

45A

0A

545.5W/ 614W

88.8%

.99

42°C/ 48°C

3.31V

5.01V

12.13V

5.05V

Test CL2

13.2A

13.2A

44A

0A

109.6W/ 132.5W

82.3%

.98

33°C/ 38°C

3.30V

5.01V

12.15V

5.05V

First, let's analyze the voltage regulation. We see a drop in the +3.3V rail,
going from +3.34V to +3.26V. That's a drop of 0.08V, or 2.4%, which is average
for a +3.3V rail that uses DC to DC for regulation. The +5V dropped from +5.03V
to +4.97V, which is a drop of 0.06V, or 1.2%, which is above average for a
DC to DC rail. The +12V dropped from +12.15V to +12.11V. This is phenomenal
as it represents a drop of only 0.04V, or 0.3%.

Next, let's look at the efficiency. Specifically, we want to look at test
2, 5 and 8 as these represent 20%, 50% and 100% loads, which is what 80 Plus
uses to judge what "grade" to categorize a PSU under. My loads are not the
same as what is used for 80 Plus. To make reviews between different power supply
makes and models fair, I use a formula to determine how much to load up each
rail. In my tests, the Dark Power Pro has an efficiency of 87.5%, 89.1% and
88.3%. That means we're efficient enough at 20% and 100% loads for 80 Plus Gold and just
shy at 50%. Given a slight margin of error, this is close enough to still call 80 Plus Gold.

Now let's retest the
power supply using 80 Plus's loads to see if we can get even closer to the 80 Plus
Gold claims made on the box.

be-quiet Dark Power P10-550W
80 Plus load tests

Test #

+3.3V

+5V

-12V

+12V

+5VSB

DC Watts/ AC Watts

Eff.

Simulated system load tests

20%

2.2A

2.2A

0.1A

7.4A

0.5A

111.6W/ 130.3W

85.6%

3.32V

502V

-12.23V

12.15V

4.99V

50%

5.4A

5.4A

0.2A

18.5A

1.2A

276.5W/ 311.2W

88.8%

3.27V

4.99V

-12.12V

12.13V

4.93V

100%

10.8A

10.8A

0.4A

37A

2.5A

549.9W/ 629.1W

87.4%

3.18V

4.92V

-12.14V

12.10V

4.78V

Having changed the loads, I'm now missing 80 Plus Gold more at 20% and 50%,
but I'm still at 80 Plus Gold levels at 100% load.

Next we're going to have a look at the ripple and noise:

Oscilloscope Measurements for beQuiet
Dark Power Pro P10-550W

Test #

+3.3V

+5V

+12V

+5VSB

Test 1

Test 2

Test 3

Test 4

Test 5

Test 6

Test 7

Test 8

Test 9 (CL 1)

Test 10 (CL2)

The +3.3V, +5V and +5VSB have almost no ripple and only a little bit of noise.
The +12V also only has a little bit of noise, but the sine wave we're seeing
shows us that we have some ripple that hasn't been smoothed out. Right off
the bat, we see 25mV. By test 5, this increases to 50mV. This is well within
the ATX specification of 120mV, but not something we see often in high end
power supplies.

Finally, we're going to have a look for overshoot transients:

Overshoot
Transient Testing for beQuiet Dark Power Pro P10-550W

Off to VSB On

VSB to Full, 12V

Off to Full, 12V

Going from full off to a full load on the +5VSB, we see a tiny little bit
of an overshoot, but nothing at all alarming. The +12V rail, both coming from
a stand by state and a full off state, has no overshoot at all. The rise time
on all of these tests are well within ATX specification.

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