What about the energy conservation. Of course there are energy leaks in AC->DC conversion if you don't take into account the heat produced during the conversion

What about the energy conservation. Of course there are energy leaks in AC->DC conversion if you don't take into account the heat produced during the conversion. If your purpose is heat, the efficiency is 100%. A radiator behaves like a very big passive cooler for your data center. You want it to be less than 60°C to avoid getting burned. That is perfect for CPU. Fans are definitely far from mandatory.