Is this (apparently fan-driven) "natural aspiration" assumption still valid when many chassis are designed to isolate the PSU airflow from the remainder of the components and draw and eject their air directly from/to the outside of the case? This may (or may not) still provide sufficient aspiration (due to heat convection) where the PSU intake vent is on the top of the case, but would almost certainly provide insufficient aspiration where the intake vent is on the bottom. The main subject of today's review will be the RM850, which, as its model number implies, has a capacity of 850 W, making it the second-strongest RM unit. Corsair says to have equipped this and all other RM units with low-noise capacitors and transformers, and a semi-passive operation, a nowadays often sought-after feature to drastically reduce noise output. Its fan is also custom-designed to operate quietly—Corsair states it to be whisper quiet, even at high load. Our dB meter will clearly show whether this holds true. The Corsair RM series power supplies are designed to run without active cooling for up to 40% load at typical room temperatures (25°C, or 77°F) and are capable of continuously outputting 100% of output capability at ambient temperatures of up to 40°C (104°F). We have found that our power supplies are typically used in environments much lower than 40°C and tend to have some natural aspiration within the chassis that allows for some air movement, such as from a nearby graphics card or chassis fan, within the PSU housing, when temperatures exceed normal room temperatures. We have found that this normal aspiration can maintain Corsair’s Zero-RPM fan-less mode even at temperatures as high as 35°C (95°F) when only at 40% load for durations of up to 15 minutes. We have found that our power supplies are typically used in environments much lower than 40°C and tend to have some natural aspiration within the chassis that allows for some air movement, such as from a nearby graphics card or chassis fan, within the PSU housing, when temperatures exceed normal room temperatures. We have found that this normal aspiration can maintain Corsair’s Zero-RPM fan-less mode even at temperatures as high as 35°C (95°F) when only at 40% load for durations of up to 15 minutes.