Corsair proved once again that it has the required know-how, the resources and the right partners to build amazing power supplies. The Corsair AX850 is a clear example of this since it achieves top performance in all areas: load regulation, ripple suppression and transient response. It is also the most efficient 850W unit that I have evaluated so far and one of the quietest ones, since it managed to obtain a LAMBDA-A+ noise certification by Cybenetics. This means that its overall noise output stays within 15-20 dB(A) under normal ambient temperatures (30-32C). Thanks to the highly efficient platform the fan profile can be super relaxed, without compromising the unit's reliability through time. After all, the ten-year warranty depicts Corsair's faith in this product.
While it's the best 850 watt premium PSU around, it's not a perfect device. I wish the current triggering points on the minor rails were lower, that there were a larger distance between the peripheral connectors (ideally 150mm) and that there were 16AWG gauges on the EPS connectors
The only competitor for the AX850 seems to be its rival sibling, the Seasonic Prime Titanium Ultra which loses a bit in the overall performance area, but it is even quieter. The EVGA SuperNOVA 850 T2 might be dead silent as well and it also achieves a good overall performance, but it is no match to the aforementioned units.
If you don't have a problem paying a premium price for one of the best 850W units that money can get you today, the AX850 seems an ideal choice. Its only strong competitor, the Seasonic SSR850TD-Ultra is a few bucks more expensive offering about the same performance levels and a bit quieter operation, which most likely will pass totally unnoticed by the majority of users.
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Disclaimer: Aris Mpitziopoulos is Tom's Hardware's PSU reviewer. He is also the Chief Testing Engineer of Cybenetics, and developed the Cybenetics certification methodologies apart from his role on Tom's Hardware. Neither Tom's Hardware nor its parent company, FuturePLC, are financially involved with Cybenetics. Aris does not perform the actual certifications for Cybenetics.