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 three electronic loads (Array 3711A, 300W), a Rigol 1052E oscilloscope and a CEM DT-8852 sound level meter. In the near future we plan to acquire six additional loads to complete 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 ZM850-HP 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 ZM850-HP. 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.


Although Zalman states that the maximum operational temperature is 40°C the PSU worked flawlessly at 53.3°C ambient and with full load. Efficiency peaks at 88.69% with 60% load and throughout 20-80% load is constantly above 88%. Power factor readings are low and with 20% load the PSU does not pass the 0.9 limit that the 80PLUS Silver certification requires. Even with 100% load PF does not reach close to 0.99. It seems that excess heat has a big impact on the performance of the APFC circuit.

Voltage regulation at +12V registered 1.36% deviation at 5V 2.28% and only the 3.3V rail went above 3% with 3.77% deviation. To sum up voltage regulation at 12V is pretty tight, at 5V well under the 3% mark while the 3.3V rail stays within the 5% deviation that the ATX spec requires.

Efficiency at Low Loads

In the next tests, we measure the efficiency of ZM850-HP 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 loads below 90W does not pass the 80% mark, which is a below average result.

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).


In standby mode the PSU consumes only 0.55W, about half of the 1W limit that ErP Lot 6 (2010) sets as maximum energy consumption during off state or standby.