Working together with our APC SmartUPS SC 620, the X-650 was stable at loads up to 412 watts when powered by the mains but could only switch to the UPS’s batteries at loads up to 302 watts. The numbers for the X-850 are 403 and 300 watts, respectively.
It’s impossible to find fault with the cross-load stability of these PSUs. The +12V voltage is always within 1% of the required level whereas the other voltages are within 2%.
Thus, the newest Gold-certified PSUs from Seasonic are superior in this test to their predecessors which couldn’t always keep their voltages within the 3% range as promised by the manufacturer.
Output Voltage Ripple
The newest PSUs from Seasonic were superior to their predecessors in the previous test but things aren't so bright here.
The high-frequency voltage ripple is within the permissible limits, yet stronger than with the previous PSUs of this series. By the way, the SS-650KM3 (X-650) and SS-850KM3 (X-850) perform in the same way here, so we only show you the graph of the higher-wattage model.
The output voltage ripple at the double mains frequency is rather weak with the X-650.
The low-frequency voltage ripple of the X-850 is weak on the +3.3V and +5V rails but strong on the +12V rail. It is always within the norm, though.
Temperature and Noise
As the previous Gold-certified PSUs from Seasonic, the SS-650KM3 (X-650) and SS-850KM3 (X-850) use a Sanyo Denki San Ace 120 fan (part number: 9S1212F404; rated speed: 2200 RPM). Such fans are perfectly balanced to minimize their operating noise.
The new PSUs feature a switch to select the operating mode of the fan between Normal and Hybrid. In the Normal mode the fan works always, starting up at low speed and then accelerating at higher loads. In the Hybrid mode the fan is idle at low loads and only works constantly at high loads.
So, in the Normal mode the fan of the X-650 starts up at a speed of 830 RPM and begins to accelerate at a load of 550 watts only. The acceleration is rapid, adding more than 400 RPM to the fan’s speed over a load range of 100 watts, yet even the resulting 1300 RPM doesn’t sound uncomfortable thanks to the high quality of the fan.
In the Hybrid mode the fan is idle until a load of 400 watts and then begins to turn on occasionally. It is only at loads above 500 watts that it works constantly. Its top speed is the same 1300 RPM as in the Normal mode.
The X-850 is expectedly louder at high loads just because its wattage is higher.
In the Normal mode the initial speed of the fan is somewhat lower compared to the 650W model and the fan accelerates at a somewhat higher load. Anyway, the X-850 is noisier than its cousin at full load as its fan rotates at 1700 RPM (which is comparable to its predecessor's result, by the way).
As for the Hybrid mode, the X-850 behaves like the X-650. The fan accelerates sooner than in the Normal mode but not so rapidly, reaching the same top speed in the end.
The two PSUs are very quiet at medium loads (even absolutely silent in the Hybrid mode). It is only at high loads (above 600 watts) that their fans remind you of their existence but we doubt that the PSU is going to be the computer’s main source of noise then.
Efficiency and Power Factor
At the reference loads of 20%, 50% and 100% the X-650 was 90.6%, 92.9% and 90.5% efficient. Its peak efficiency of 93.4% was observed at a load of 311 watts. We can also note that its efficiency was higher than 90% at any load above 120 watts.
The power factor is just a little lower than the promised 99% at high loads.
At the reference loads of 20%, 50% and 100% the X-850 was 91.8%, 93.3% and 89.8% efficient. Its peak efficiency of 93.5% was observed at a load of 435 watts. We can also note that its efficiency was higher than 90% in a load range of 100 to 830 watts.
The power factor was 99% at high loads.
Overall, the PSUs are a little more efficient compared to their predecessors.
The standby voltage of each PSU is normal.