Test Setup

All measurements are performed utilizing ten electronic loads (seven Array 3711A, 300W each, and three Array 3710A, 150W each), which are able to deliver over 2500W of load and are controlled by a custom made software. We also use a Picoscope 3424 oscilloscope, a CHY 502 thermometer, a Fluke 175 multimeter and an Instek GPM-8212 power meter. Furthermore, in our setup we have included a wooden box, which along with a heating element is used as a Hot Box. Finally, we have at our disposal four more oscilloscopes (Rigol 1052E and VS5042, Stingray DS1M12 and a second Picoscope 3424) and a CEM DT-8852 sound level meter. In this article you will find more details about our equipment and the review methodology we follow. Finally, if the manufacturer states that the maximum operating temperature of the test unit is only 40°C then we try to stay near this temperature, otherwise we crank up the heat inside the hotbox up to 50°C.

Voltage Regulation Charts

The following charts show the voltage values of the main rails, recorded over a range from 60W to the maximum specified load, and the deviation (in percent) for the same load range.

5VSB Regulation Chart

The following chart shows how the 5VSB rail deals with the load we throw at it.

Efficiency Chart

In this chart you will find the efficiency of VP550P at low loads and at loads equal to 20-100% of PSU’s maximum rated load.

Voltage Regulation and Efficiency Measurements

The first set of tests reveals the stability of voltage rails and the efficiency of VP550P. The applied load equals to (approximately) 20%, 40%, 50%, 60%, 80% and 100%, of the maximum load that the PSU can handle. In addition, we conduct two more tests. In the first we stress the two minor rails (5V & 3.3V) with a high load, while the load at +12V is only 2A and in the second test we dial the maximum load that +12V can handle while load at minor rails is minimal.


The VP550P exhibited within 3% voltage regulation on all rails, something very impressive and hardly expected from a PSU of this price range. Efficiency peaks at 84.35% with 40% load and strangely it starts (20% load) and ends (100% load) with exactly the same percentage, 81.48%. Talk about coincidence here!
The 120 mm fan, judging from the delta between input/output temperature, does a good job of moving the heat out of the case but it makes a hell of a noise. The good thing is that it doesn't produce a high pitch noise but a low frequency hum. However this hum is really loud and could be heard even when the loaders' fans kicked in and believe us, these are really loud!

Efficiency at Low Loads

In the next tests, we measure the efficiency of VP550P at loads much lower than 20% of its maximum rated load (the lowest load that the 80 Plus Standard measures). The loads that we dial are 40, 60, 80 and 100W (for PSUs with over 500W capacity). This is important for scenarios in which a typical office PC is in idle with power saving turned on.


We admit that we didn't expect ground breaking performance here but with 40W load, efficiency is really low, actually among the lowest we have ever measured! In the next three tests efficiency varies at normal levels, for a merely 80 PLUS standard unit.

5VSB Efficiency

ATX spec states that the 5VSB standby supply's efficiency should be as high as possible and recommends 50% or higher efficiency with 100mA load, 60% or higher with 250mA load and 70% or higher with 1A or more load.
We will take four measurements, three at 100 / 250 / 1000 mA and one with the full load that 5VSB rail can handle.


Efficiency at 5VSB is above the equivalent limits in all tests. The highest efficiency level is achieved, as we expected, with full load (2.5A) and it's close to the 80% mark.

Power Consumption in Idle & Standby

In the table below you will find the power consumption and the voltage values of all rails (except -12V), when the PSU is in idle mode (On but without any load at its rails) and the power consumption when the PSU is in standby (without any load at 5VSB).


Phantom power is really low so the PSU easily meets the ErP Lot 6 requirements. In idle, a mode you won't encounter in real life scenarios, at least with the PSU installed in a system, the cooling fan's consumption boosts power consumption.