ltdoc

The usual reasoning for adding capacitors to a power system is correct for as far as it's explained, but the explanation doesn't go far enough. Yes, a capacitor can 'dump' a fairly large surge of energy into a system, but then you have to allow for the recharging of that capacitor if it's ever going to be able to do another energy 'dump'. It has to get that re-charge from somewhere, and that somewhere is the alternator feeding the system. That means that if that alternator isn't fairly 'hefty', larger than stock, it's not going top be able to keep up with the demand. That means that the 'slack' has to be taken up by the battery. And that just adds another 'draw' on the alternator for recharging. Sort of a you can pay Peter instead of Paul, but Paul is still owed his due, so it's NOT a viable 'work around', you are not 'saving' anything at all. If you have a large enough energy storage system (batteries), and if the energy/power source is run continuously, then a capacitor might be of some benefit. That's not the usual case, so why bother? Those instances where a capacitor can supply the required energy are only short duration, infrequent instances.
The other side of that 'coin' is that large capacitors are dangerous! If that capacitor's voltage rating isn't 2 to 5 times as much as the normal voltage of the system, you are going to have a very loud and forceful surprise in your future. Exceed it's voltage capacity and they will explode. For instance, dead battery and you get a surge while getting a 'jump' from a friend. Bang! You honestly don't want to be near the thing. And you had better have paid your insurance premium!
Have fun.
- 'Doc

mrarff

What you have plain and simple is a bad ground, inadequate size wire, or a "ghetto" install. Or you may just be trying to bust out the windows. I have a 1000 watt sub amp, and a 400 watt amp for the door speakers. All this on a 5 year old stock battery, and I have never had a problem!. Check out my gallery for picks of my install.