I've been wondering, if my system draws about 400W at peak, which PSU would be quieter? assuming both are from the same manufacturer using the same type of fan and cooling mechanism? My theory was the 1200W PSU would be quieter, because it's only running at roughly 33% load, versus a 600W PSU running at 66% load. Has anyone ran a test of this scenario?

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    There is no telling which one is quieter. For all we know the 1200 Watt PSU has two fans and the second one only kick in under high load. (The first fan could be identical to the fan in the 600 W version). -- TL;dr. There is not one single clear answer. – Hennes Mar 28 '13 at 15:54
  • Yes, but my theory is that manufacturers has logic that sets RPM at a certain load level, so 1200W at 33% would be spinning slower than the 600W at 66% load, and usually slower RPM will result in less noise. Though I don't know if this theory is true in practice. – KoKo Mar 28 '13 at 15:57
  • It could well be true for many, or even most PSU's. But there is no sane way to compare any 600W PSU with any 1200 Watt PSU and make a safe prediction. You will have to compare specific models. – Hennes Mar 28 '13 at 16:03

If this is an abstract question, I'd say that nothing changes. If the two PSUs have the same components and cooling mechanism, since the power drawn is the same, I expect the heat produced would be the same, so the fan should spin at the same speed on the two PSUs.

Also, consider that a PSU has its maximum efficiency when it is run at about 60-80% of its maximum and the efficiency diminishes with load. This means that more energy is lost in the circuitry (in form of heat). A 1200 W psu would be tuned for maximum efficiency at a higher power, so it would be less efficient than a 600 W PSU at 400 W.

In a real scenario, I'd also take into account that a 1200 W PSU might have better components than a 600 W PSU from the same manufacturer, to ensure better stability at higher power loads. This could bring better overall efficiency and reduce the heat produced, and thus the fan speed.

To have a more experimental answer to the question, you can read these two reviews of the same PSU model (550 W and 1200 W) performed by the same website. Unfortunately the fan noise is below the least audible level for both the PSUs, but you can see that the fan noise only increases when the 1200 W PSU is loaded with more than 900 W.

  • Thanks, my own experiment also confirms that when I put 700W usage on the 1200W PSU, the fan starts to be noisy. So overbuying PSU capacity would indeed reduce noise if I wanted a quiet build. – KoKo May 2 '13 at 1:48
  • @KoKo This is true in principle. In practice, I think that it is better to buy an high quality PSU that is designed to handle the required power, rather than overbuying PSU capacity, for the efficiency reasons that I pointed out in my answer. – Pincopallino May 3 '13 at 9:21

I'd say if you want a quiet system get a fanless psu instead so long as you have sufficient airflow through your case. Tom's Hardware reviews some here http://m.tomshardware.co.uk/power-supply-silent-passive,review-32488.html

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