The ROG Strix 650 uses a good Seasonic platform, so its high performance in almost all areas is not surprising. Moreover, Asus asked for several modifications in this platform, which allow for a dead silent operation. Compared to the older Seasonic Focus Plus Gold model (a newer version is available but we haven't tested it), the ROG Strix model is notably quieter.
This means that the large heat sinks indeed make a difference and play their role in keeping the overall noise output low, despite the double ball-bearing fan. This is the only PSU in this category, using a DBB fan instead of a rifle or fluid dynamic bearing, which are less noisy but don't live long under high operating temperatures.
The ROG Strix 650 is a good power supply, but it has several shortcomings, with the most significant being the high asking price. The short distance between several of its peripheral connectors can also create compatibility issues with some chassis.
Moreover, we would like to see a more efficient 5VSB rail, higher efficiency at super-light loads, and compatibility with the alternative sleep mode, to be fully compliant with the upcoming ATX spec's requirements. With less money, you can get a Seasonic GX-650 or the Corsair RM650x, with the latter achieving higher performance, and also having notably lower noise output. If its price drops or you find one on sale, the ROG Strix 650 would be a much better value relative to its competitors.
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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, Future PLC, are financially involved with Cybenetics. Aris does not perform the actual certifications for Cybenetics.