Pico PSU - http://www.mini-box.com/s.nl/it.A/id.417/.f
As silent as the power brick you use, and up to 98% efficient (though you won't find a 100% efficient power brick so realistically you can expect near 80% efficient).
If you have an old 12V power brick laying around that puts out 9A you are set. Or, you could buy one. Or if you have some other voltage they have a version that takes inputs from like 12-25V.