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 GX650W 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 GX650W. 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 good news first. Efficiency is high enough for the category of the PSU (80 Plus Bronze) and full load operation even at 50°C is possible, although the manufacturer states that 40°C is the max operating temperature.

A strange thing that we observed was that the +12V rail voltage started low at 20% load, went up till 50% load and only with higher loads started going down, which of course is normal. Group regulation is responsible for this weird phenomenon. Regarding voltage regulation deviations, at +12V it's 2.5%, at 5V a little below 4% and at 3.3V exceeds the ATX limit of 5%. Overall voltage regulation is loose and especially on the minor rails we wanted to see closer or even under 3% deviations.

We saved the bad news for last. The unit performed terrible during Crossload tests. At CL1 test +12V and 5V went out of bounds and 3.3V was very close to the lower limit. At CL2 test, although we pulled less power than the maximum that the manufacturer claims, the +12V rail dropped extremely low reaching the lower limit that ATX spec defines for this rail, 11.4V. Of course from a group regulated PSU with 650W capacity we didn't expect a lot, maybe Cooler Master should revise their performance claims.

Efficiency at Low Loads

In the next tests, we measure the efficiency of GX650W 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.


Efficiency at low loads is quiet good. At 65W load it is very close to 80% and with 89W it surpasses the latter mark by almost 3%. Overall GX650W performed very well here, especially if we take into account that it is only 80 Plus Bronze certified.

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).


With only 0.45W the unit is ErP Lot 6 ready and will be ready in 2013 too, when the limit will come down to 0.5W.