Pros, Cons And Final Verdict
CWT, under Corsair's guidance, manufactures several excellent PSU families, including the RMi and RMx. The only differences between them is the lack of a digital interface and a rifle bearing fan in the RMx models, which push their prices down. Indeed, many enthusiasts don't care about the RMi's digital goodies, preferring simpler (and less expensive) alternatives. I personally believe that the ability to monitor a PSU's operation and control its fan is important. But I also understand that not everyone shares my opinion.
Regardless, the RMi line-up doesn't even include a 550W member, so the RM550x stands alone in Corsair's portfolio. The competition is pretty compelling; EVGA's 550 G2 is probably the most noteworthy opponent. Compared to that power supply, the RM550x features even better performance and quieter operation. In fact, Corsair's offering more closely resembles a passive PSU than a normal one. Its semi-passive operation lasts for a long time, and even when the fan engages, it spins slowly. We had to push the PSU very hard to get its fan to register more than 30 dB(A). Normally we would be a little skeptical about the reliability of a PSU without heat sinks on its secondary side and such an unobtrusive fan. However, Corsair appears to be very confident in CWT's design. Otherwise it wouldn't equip the RM550x with a seven-year warranty.
The RM550x is an amazing PSU with fantastic ripple suppression, tight load regulation on the minor rails and excellent performance with transient loads. The cherry on top is nearly silent operation. On top of that, this unit is highly efficient, although some other Gold-rated PSUs with similar capacity fare a bit better. Another advantage of the RM550x is the quality of its internal components. The only thing that we would like to see in this PSU is a convenient way to test the fan's proper operation. The fan does spin for a short time every time the power supply is switched on, but we'd like Corsair to add a fan test button like the one on its RMi units.
In general, it is really hard to find any flaws in a PSU like this. We're extra-picky though, so we would like to see even tighter load regulation on the +12V rail. Finally, it would be nice if Corsair dropped its price closer to 90 bucks. That'd increase the RM550x's performance per dollar ratio, bringing its value more in line with EVGA's 550 G2, which previously dominated the mid-wattage category alongside the 650 G2.