I found a bit of info that might help from ......http://www.audiogroupforum.com
V = IxR. Where: V = Voltage I = Current. R = Resistance
With a power amplifier, resistance varies with the volume and frequency of the music. As the resistance fluxuates the amp draws more current and expects the voltage to remain the same. It is the regulator on your alternator's job to make sure the voltage stays the same by dishing out more current when it is needed. If the regulator cannot react fast enough to the change in resistance, the voltage will drop.
This means, each time there is a bass thump, the voltage will drop slightly until the regulator catches up. You will recognize this at night by seeing your lights flicker. The regulator is fast acting, but not as fast as a double bass drum.
A capacitor tricks the alternator's regulator into thinking there is less resistance while the amp is in a low-output state by storing electrons and creating a faux current. When the amp changes to a high-output state, the capacitor is quickly drained and begins to charge again when the amp switches back to a low-output state. This happens very quickly...such as between bass drum kicks in a fast rock song.
The result is a smoother current draw from your alternator which prolongs the life of the regulator. There is also an audible difference in music because the voltage will not fluxuate as much and your amps will get the current they want...when they want it.
However, many new amps use regulated power supplies to combat this fluxuation in voltage. This means whether your alternator runs at 15 volts or 11 volts, the amp will operate the same. Essentially, they don't take advantage of the extra voltage when it is there. For this reason, a regulated amp will have higher SQ while an unregulated amp will have higher output while the car is running (14v) vs. while the car is not running (12.5v).
Still, a regulated amp will cause a fluxuation in current even if it unaffected by the drop in voltage meaning a capacitor can still help your electrical system.