I just read about two PSUs that I have yet to see a review or recommendation on silentpcreview. Since these power supplies were reviewed by an Australian site, perhaps they are not readily available in the United States, but I see no reason why not if they are quality components. The first PSU is the Just Cooler SP-300 300W, reviewed here and Thermaltake's 420W Silent Pure Power, reviewed here. As to how quiet they are relative to other PSUs reviewed by silentpcreview, I have no idea, but I'd certainly like to know, since I'm itching to get a new, relatively cool (no pun intended) and quieter ready made solution soon.

We contacted Just Cooler / Orbitron many months ago for review samples and they told us they could sell and ship them to us from Taiwan at our cost. AFAIK, they don't have distribution in the US or Canada. The documentation they supplied was sparse, and no noise figures were provided, not even a fan make/model. Even though their PSU could be quiet, I doubt they would complete against the quiet champs here. The main advantage of centrifugal blowers is not low noise per se, but their good noise/airflow ratio and the directionality of the exhaust airflow.

With the Thermaltake, well, it has 2 fans. If you keep everything else exactly the same as, say, a Zalman or Seasonic, except for the the 2nd fan, you will get 3 dB more noise from the 2nd fan. Then you'll get 2-3 dB more noise from the turbulence of that 2nd fan's airflow in the PSU. So let's say 5 dB. Most people will hear that as close to 50% louder. The Antec truePower series PSUs are very quiet for 2-fan modesl -- they are the quietest 2-fan models I have heard. But they are substantially louder than any of the quiet 1-fan models I've reviewed.

Does that help answer your questions?

http://www.dansdata.com/sp300.htm dansdata reviews the same PSU here as well, he doesn't like it at much, like it's claimed bug protection properties like heck! and the way the blower is setup is just a axial fan in a blower casing, that would cut down the airflow of the axial fan