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 EPM1200EWT 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 EPM1200EWT. 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 is very high in all load tests, despite the high ambient inside the hotbox. Seven out of the eight readings are above 90% and three of them are above 92%. The peak is registered at 40% load with an impressive 92.99%. Currently this is one of the highest efficiency readings we have ever seen. Continuing with the positives, the 5V rail registered tight enough voltage regulation for our standards and the 3.3V is decent. On the contrary the +12V rail was loose with a deviation reaching 3.6%. Apparently Enermax focused on efficiency and put +12V voltage regulation as second priority. We would prefer a balanced situation since 3.6% puts EPM1200EWT in the last place among similar capacity units. Finally the unit's ability to withstand extreme ambient temperatures impressed us since even at 51.0°C it managed to complete the demanding CL2 test.

Efficiency at Low Loads

In the next tests, we measure the efficiency of 51.0°Cat 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.


Even at low loads the EPM1200EWT registers high efficiency. In the two last tests the 80% mark is easily passed and even with only 40W load efficiency is clearly over 70%. Overall this PSU can be characterized as an efficiency champion since regardless the load level it manages to achieve the highest possible efficiency that its capacity allows.

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.


Same story here. The high-end standby PWM controller along with the rest components of the fly-back converter make 5VSB highly efficient and at test#4 we measured an impressive 85%.

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 very low, at mere 0.22W so this unit easily meets the ErP Lot 6 2010 and the future 2013 requirements. The latter demands a power consumption equal or less of 0.5W at standby, without any load on the 5VSB rail.