Working together with our APC SmartUPS SC 620, this PSU was stable at loads up to 405 watts when powered by the mains but could only switch to the UPS’s batteries at loads up to 290 watts.
The X-1050 is somewhat worse in this test than the above-discussed models, its +12V voltage being more than 1% off the required level at low loads. When there's high load on the other rails, the +5V voltage is more than 2% off. On the other hand, this PSU is better than earlier X series products in this respect.
Output Voltage Ripple
The high-frequency voltage ripple is comparable to the new models we’ve tested above (it’s somewhat stronger on the +12V rail and weaker on the +5V rail) but worse compared to earlier Seasonic products.
The low-frequency ripple is rather strong on the +12V rail (as with the above-discussed PSUs) and on the +5V rail, but always remains within the permissible limits. It’s weak on the +3.3V rail.
Temperature and Noise
As the KM3 series discussed above, this model is cooled by a Sanyo Denki San Ace 120 fan (part number: 9S1212F404, rated speed: 2200 RPM) and offers a switch to choose between Normal and Hybrid operating modes.
In the Normal mode the fan behaves like in the above-discussed PSUs except that its initial speed is very high at almost 1100 RPM. The fan reaches its rated speed of 2200 RPM at a load of 900 watts.
It is only at loads below 700 watts that this PSU stays quiet.
The Hybrid mode is only good at extremely low loads. The fan turns on periodically even at loads of 100 watts and works constantly at 300 watts and higher. And its initial speed is over 1000 RPM, just like in the Normal mode.
There is a sudden increase in speed at 600 watts, the fan reaching its top speed by 900 watts - exactly as in the Normal mode.
Frankly speaking, the cooling system of this PSU left us disappointed. The initial speed of the fan is too high and the stretch of passive cooling in the Hybrid mode is too short. That’s not like other Seasonic PSUs, so we even suspected our sample to be defective. However, reports from users and other reviewers agree with our test results.
Efficiency and Power Factor
At the reference loads of 20%, 50% and 100% this PSU was 90.2%, 92% and 88.5% efficient. Its peak efficiency of 481 watts was observed at 93.1%.
The efficiency is somewhat lower compared to the above-discussed PSUs, which can be explained by the difference in wattage. Higher-wattage PSUs are generally less efficient than their lower-wattage counterparts. So, whatever the reason, Seasonic's newer KM3 series PSUs are more efficient.
The power factor is close to 99% at high loads.
The standby source copes with the specified 3A load easily.