The specs are consistent with those of the junior model and meet today’s requirements. The SSR-550RM can deliver most of its power via the +12V rail while the combined load capacity of the +3.3V and +5V rails is only 100 watts.
The standby source can handle loads up to 2.5 amperes, as is typical of midrange PSUs.
Like the previous model, the SSR-550RM complies with the 80 PLUS Gold standard.
The SSR-550RM showed better compatibility with UPSes than its junior cousin. Working together with our APC SmartUPS SC 620, it was stable at loads up to 382 watts when powered by the mains and could switch to the UPS’s batteries at loads up to 325 watts.
Cross-Load Voltage Stability
Like with the junior model, the +12V voltage fluctuates by 2% at low loads. It gets more stable than in the Seasonic SSR-360GP at higher loads, staying within 1% of the required level.
The +5V voltage is within 1% of the required level at most loads. As opposed to the Seasonic SSR-360GP, the 2% zone in the diagram is in the area of low rather than high loads on all of the power rails.
The +3.3V voltage is the least stable of all. When there’s very low load on each power rail, it even goes beyond the promised limit of 3%. It's no big problem, though.
Overall, we can’t really find any fault with the cross-load stability of the SSR-550RM.
Output Voltage Ripple
Compared to the junior model, the high-frequency voltage ripple is stronger on the +12V rail but somewhat weaker on the other rails.
There’s almost no voltage ripple on the +12V rail at the double mains frequency, though.
Thus, the output voltage ripple of the SSR-550RM is higher than with Seasonic’s more advanced PSUs but meets the requirements of the industry standard.
Temperature and Noise
The SSR-550RM is cooled by a 2050RPM ADDA AD1212MB-A70GL fan.
The fan is regulated like in the previous model except that it accelerates later and smoother. It is only at 350 watts that the fan reaches 1000 RPM and becomes uncomfortable. In the SSR-360GP, the fan speed is as high as 1800 RPM at such a load.
Well, the SSR-550RM eventually makes its fan work at 1800 RPM, too, but only at loads of 500 watts and higher.
Thus, the SSR-550RM is better than the SSR-360GP in terms of acoustic comfort. It is silent at loads up to 300 watts, very quiet at up to 350 watts and only becomes uncomfortable at loads above 400 watts.
Efficiency and Power Factor
The SSR-550RM was 88.5%, 92.3% and 90.8% efficient at loads of 20%, 50% and 100%, respectively. The peak efficiency of 92.4% was observed at a load of 309 watts.
The power factor is above 99% at 50% load, reaching a maximum of 99.8%.
The standby source copes with its job without any problem.