"Ask Doctor Emmett Brown", that's funny as hell
when it comes to car audio all you care about is the RMS wattage (continuous) not the peak/max because they mean nothing
if you are having charging issues a cap wont help
you need to start by upgrading the size/gauge of your power wires in your sound system
if that does not solve the problem you will need to do the big 3, which is upgrading the wires in the charging system (battery/ alternator, ground)
last but certainly not least is to get a H.O. alternator (high output)
a cap is like a VERY small battery, and as you know your sounds' power does not come from the battery unless the car is off, when the car is running the power comes from the alternator which keeps the battery charged