<< 50AMP might be a little much. I have run my 100watt Car amp off a 10AMP Redundate PS for over 6 months >>
depending on your amplifier, 50 amps could be too little
My car amp is rated at 60amps with two 30amp fuses
edit: look in Sears for a BIG power supply
or you could bring in a car battery and charge it every night