I assume this is a car audio amp that you are trying to run off AC power. The size of the DC power supply depends on how loud you want. If you have a just barely audible sound then you need maybe a 5 or 10 amp power supply. But if you want to max it out then you probably want about an 100 to 120 amp 12VDC power supply and a really large capacitor in the circuit to handle the surge. Autos have 12V batteries that can deliver 100s of amps as the capacitor. You won't have that in an AC powered situation.