Test Setup

All measurements are performed utilizing a custom designed and built load tester, called Faganas, which is able to stress PSUs up to 1800 Watts. We also use a DS1M12 (Stingray) 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 nine electronic loads (six Array 3711A, 300W each, and three Array 3710A, 150W each), a Rigol 1052E oscilloscope and a CEM DT-8852 sound level meter. In the near future the electronic loads will form our new test set up, which with the help of our custom built software will have the same capabilities with the, ultra expensive, Chroma ATEs. In this article you will find more details about our equipment and the review methodology we follow.

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), when compared with the voltage values at 60W load.

Efficiency Chart

In this chart you will find the efficiency of RAPM550 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 RAPM550. 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 the maximum load that our tester can apply to these rails, 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 minimum.


Let's start with the positives first: the PSU manages to deliver its full power even at 50°C ambient and efficiency peaks at 40% load with an impressive 85.99% reading, a very high number for a plain 80 PLUS unit. We can pretty much say that all goes well until we dialed 100% load. Then suddenly the +12V rail registers a huge voltage drop, showing clearly that it cannot handle the extra load well and 3.3V rail goes out of ATX spec. On top of that efficiency drops by a huge 2.4% percentage. As it seems RAPM550 going from 450W to 550W is stressed pretty hard, so it would be better if it was labeled as a 450W PSU. Then voltage regulation on all rails along with efficiency would be much better. Finally, the CL1 test showed weaknesses of the group regulation design and the fail in CL2 test proves that +12V cannot handle the load that the manufacturer claims, since we pulled around 470W from +12V at this test and power specs say that the same rail can deliver up to 480W, a very optimistic number according to our readings.

Efficiency at Low Loads

In the next tests, we measure the efficiency of RAPM550 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 (approximately) 40, 65 and 90W. This is important for scenarios in which a typical office PC is in idle with power saving turned on.


If we take into account the efficiency certification of this PSU then at low loads it performed pretty well since with 63.57W load, efficiency almost reached 80% and with 88.47W load it registered an impressive 83%.

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).


Our power meter measured very low phantom power so RAPM550 is definitely ErP Lot 6 ready (<1W at standby mode).