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 MK3S400 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 MK3S400. 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 with 20% load is a little low, even for 80 PLUS Bronze standards. Normally for this efficiency rating and with 230VAC power input, the lowest we should see at 20% load is 83-83.5%. On all other load levels efficiency is high enough though, for a Bronze unit. Voltage regulation at +12V is very tight, under 1% and on the minor rails it's between 3-4%, not bad for the category this PSU belongs to. Also as you can see from the 100% load test the unit has no problem at all delivering its full power even at 50°C ambient. The fan during this test was surely audible but we wouldn't describe it as annoyingly loud. Finally, the horrible performance at the unrealistic CL1 test is the result of the group regulation design used in the secondary side of this unit. Thankfully the performance at CL2 test, which is a more likely to happen scenario in a modern system, is much better.

Efficiency at Low Loads

In the next tests, we measure the efficiency of MK3S400 at loads much lower than 20% of its maximum rated load (the lowest load that the 80 Plus Standard measures). The loads that we dialed at this case were 40, 50, 60 and 70W since the PSU has small capacity. This is important for scenarios in which a typical office PC is in idle with power saving turned on.


In loads below 80W this PSU plays in its field thanks to its low capacity. With 40W and 50W load efficiency is over 75% and with 60W and 70W it easily surpasses the 80% mark. So in a small system with low power demands this unit would fit like a glove. Many higher efficiency rating PSUs, with higher capacity too, cannot even surpass 80% efficiency at such low loads.

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.


On the 5VSB rail efficiency is constantly above the ATX spec recommended levels. At test#4 efficiency is marginally lower than test#3, indicating that 2.5A are very close to 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).


Phantom power is very low, at 0.1W, so the MK3S400 easily meets the ErP LOT 6 2010 (and the future 2013) directive.