We're partial to Seasonic's fanless ATX power supplies but even their 450W model is overkill for most fanless builds (which usually don't include a graphics card). Akyga launches four new fanless PSU including a very interesting 300W model, as well as 400W, 500W, and 600W units. Rated 80 PLUS and fully modular, these power supplies should be available in Europe in the coming weeks.
Source: Akyga
