You should be able to use the 12V coming out of the power supply. However, to reduce noise, I would use the 12V from the power supply to activate a relay that provides the 12V (from the battery) to the amp. Or, you can use the ACC line from the car that is switched on only when the car is running. That would have the amps on whenever the car is running, but if you're like me, if the car is running, I'm listening to something. Hope that helps.