The Corsair RM850x (2018) PSU Review: Exceptional Electrical Performance

Hot Test Results

Even though Channel-Well Technologies is better known for their cost-effective designs, the platform that they developed for the RM850x has rather outstanding electrical performance. Even when subjected to high ambient temperatures, the power quality of the RM850x is fantastic, with a maximum ripple of just 12 mV on the 12V line under maximum load. Furthermore the maximum ripple recorded on the 3.3V and 5V lines does not exceed 12 mV either. The voltage regulation is fantastic too, with the all of the voltage lines staying within 0.6-0.7% across the nominal load range.

These figures are extremely low for a unit with this kind of output, regardless of its retail price. We have only tested a handful of products that can compete with the new RM850x in terms of power quality and they all were significantly more expensive.

The impact of high ambient temperature is not apparent when looking at the power quality figures but the conversion efficiency drop is significant, especially under heavy loads. With an ambient temperature between 45 °C and 50 °C, the average nominal load (20-100%) efficiency drops down to 90.2%/88.1% during this test with an input voltage of 230V/115V AC respectively. The drop is not consistent across the entire load range, with the RM850x performing significantly worse when heavily loaded for extended periods of time, suggesting that its active components are struggling under such adverse operating conditions.

Strangely, the thermal profile of the RM850x hardly changed at all while the unit was operating inside our hotbox. The fan did not start before the load was greater than 200 Watts but it was noticeably faster when it did, yet barely audible. This changes quickly when the load surpasses 450 Watts, where the fan's speed increases abruptly and reaches clearly audible noise levels. This is necessary to maintain reasonable and reliable operating temperatures, which the RM850x does, yet the figures are relatively high when the unit is operating at or near its maximum capacity. The RM850x should be able to maintain reliable operation under such operating conditions, yet the high temperatures clearly do have an impact on its energy conversion efficiency.