Working together with my APC SmartUPS SC 620, this PSU was stable at loads up to 370 watts when powered by the mains but could not switch to the UPS’s batteries even at a load of 280 watts.
The +5V and the crucial +12V rail are both stable, their voltages staying within 3% of the required levels. The difference is proportional to load: the higher the load, the smaller the difference between the actual and nominal voltage level.
The +3.3V voltage is somewhat worse as it deflects from 3.3 volts sharp by 4% when there is low load on all of the power rails. Otherwise, the diagram is similar to those for the other voltages.
All in all, the NAXN ENM850EWT delivers very stable voltages.
Output Voltage Ripple
The +12V rail has clearly defined high-frequency voltage ripple, but it is very weak. The voltage ripple on the +3.3V and +5V rails is almost nonexistent.
The same goes for the low-frequency output voltage ripple.
Temperature and Noise
The NAXN ENM850EWT is cooled by an 11-blade Globe Fan (RL4Z B1352512H, 1500 RPM, 135 mm). Notwithstanding its transparent impeller, the fan lacks highlighting.
Mechanical noises could be heard at low speeds of the fan, but at high speeds it only produced pure aerodynamic noise.
The fan starts out at a speed below 850 RPM and keeps it until a load of 300 watts. The speed grows linearly afterwards, reaching the subjectively comfortable limit of 1000 RPM at a load of 450 watts. The fan is rotating at 1400 RPM at full load, which is lower than the top fan speed of most other PSUs.
The NAXN ENM850EWT is somewhat better than most other PSUs in terms of noisiness. A special feature of this PSU is that its fan keeps on rotating at a low speed for a while after the PSU has been shut down. This helps cool the components better.
Efficiency and Power Factor
The power factor is somewhat inferior to that of most PSUs with active power factor correction.
The efficiency is far from record-breaking but meets the 80+Bronze requirements by some margin. The NAXN ENM850EWT was 85%, 87.7% and 84.7% efficient at the three reference loads (20%, 50% and 100%, respectively). Its peak efficiency was 88.1% at a load of 384 watts.
The standby voltage is always higher than necessary but meets the requirements of the industry standard.
The NAXN ENM850EWT lacks any extraordinary features but also has no obvious downsides. It is rather quiet and can make a good buy if you’re satisfied with its price.