A PSU gives power to the PC, with different voltages (3.3V, 5V, 12V) to suit each component. Fans work with 12V, it's the adopted standard.
So, for powering a fan you just need a source for the 12V. You can use a PSU, but it is easier to just use a
12V ADCD adapter.
The adapter will give power to the fan controller. Now, fan controllers are normally powered with 4 pin molex, carrying 12V, 5V and two grounds.
Most of these controllers only use the 12V line, but some models have a switch to enable a 5V mode. You don't need these. Just get a simple one that installs itself in a 3.5" bay. They usually have 4 pots to control 4 different fans and only use the 12V line. Perfect for use with the above 12V ACDC adapter.
You will need to adapt the ADCD adapter connector to the fan controller's power connector, but this will be easy.
