[fox46]

I am assuming that your cart has a on-board 12V battery. Just buy a 10 Amp battery charger, and have the battery on-charge while you're listening. Don't use a charger as a powersupply because the quality of power is very poor (lots of noise, and no voltage regulation - could hurt the AMP). By using a battery, it acts sort of like a reservoir in a plumbing system- It takes the erratic power from the charger (pump) and uses it to "fill" the battery (reservoir), and then you can draw as much/as little electricity (water) from the "reservoir" at the same quality as pure DC power. The battery essentially acts as a crude voltage regulator/power stabilizer.

I like sound systems on carts - post some pictures when you're done