my mate had a setup like this in his room running two 12' sub's he could also move it to cars when he wanted. The way we done it was, build a small box which held a normal car battery, and 12 power supply. We had a voltmeter and ammeter hooked up to it also. Just plug it into the wall and charge the battery, then the amp would run off the battery. This made it mobile. You could get a fair bit of listening time out of it and when it went flat just plug it into the wall and recharge it.
If it's going to be in the same place then do as the ethereal said and get a power supply to step the mains voltage down and rectify it to DC these will also have the regulating circuitry build in. Just make sure you get one that can provide enough current (depending on amp being used).You shouldn't need anything near 100A. Take a look at the fuse size in the amp (20-30A?) and get something rated below this. Do not use a car charger!=smoke
hope there's something there that helps??