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 45-50°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 AX650 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 AX650. 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.


Efficiency overall is pretty high, although with 20% load it is not up to the level we expected from a Gold efficiency PSU. Voltage regulation at +12V is below 2%, at 5V easily stays within 3% and at 3.3V it's 3.5%. Overall we were left satisfied by the unit's voltage regulation. Despite the fact that the AX650 operates in fanless mode at lower loads, inside our hotbox the fan was working from test#1 with 20% load. Until 40% load the fan was inaudible but with 50% load and at 43.6°C ambient its speed increased so it surely made its presence felt, however it wasn't annoyingly loud. At 100% load and at CL2 test the unit clearly proved that it has no problem delivering its full power even at above 50°C operating temperature. In fact the AX650 features a very cool operation and we had to leave the heating element inside our hotbox switched on for quite some time, in order to heat the PSU.

Efficiency at Low Loads

In the next tests, we measure the efficiency of AX650 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.


As we expected, efficiency at low loads is pretty high. This is why we strongly advice to use a mid-wattage PSU if you want to power a system with medium power demands. You will have significant gains in power consumption at idle and lower loads, where bigger PSUs simply cannot compete with smaller capacity ones. In this case, in three out of the four tests we ran, efficiency was way above 80%, a remarkable performance.

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.


At 5VSB, efficiency is at high levels and even at test#2 it stays above 70%, a very high reading for this amount of load (0.25A). It peaks close to 78% with the max power that the 5VSB rail can deliver.

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).


Vampire power is really low, at 0.1W, so the unit easily meets the requirements of ErP Lot 2010. Apparently the standby PWM controller does a fine job restricting power consumption at standby, at minimum levels.