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 EPM850EWT 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 EPM850EWT. 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.


The unit outputs very little heat, a common characteristic of all Platinum efficiency PSUs and we had to leave the heating element on for quite long in order to achieve high enough ambient inside the hot box. Let's start with the most interesting feature of Platimax, its efficiency; as you can see with 20% load it is a little low for Platinum standards but with 40% load it launches to nearly 92% and stays there till 60% load. Even at full load the unit scores an impressive 90.6% efficiency despite the 47.3°C ambient. Not bad at all although we would like to see higher efficiency at 20%, since with 230VAC efficiency is 1-1.5% higher than with 115VAC power input. However we should not forget that our tests are conducted with much higher ambient than the 23°C temperature at which 80 PLUS organization certifies all units and as ambient goes up efficiency goes down.

As for voltage regulation the Platimax for sure didn't score very high, especially at 3.3V where it nearly touched the 5% limit but at least +12V stayed within 2%. Finally we should note here that the fan was fairly quiet even at high loads/temperatures, rendering this PSU suitable for silent computing fans.

Efficiency at Low Loads

In the next tests, we measure the efficiency of EPM850EWT 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.


Efficiency at low loads is good enough since even with 40W load the PSU manages to stay well above 70%, at 60W it almost reaches 80% and from 80W and above, it surpasses the aforementioned mark with ease.

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.


Strangely enough in test#2 efficiency is lower than test#1; nevertheless in both cases it is above the equivalent limits. The same goes for tests #3 and #4 where efficiency is over the 70% mark. In general the PSU has satisfactory efficiency at 5VSB since it manages to surpass the ATX spec limits in all cases.

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 so the Platinum Enermax easily meets the ErP Lot 6 requirements, current and future ones.