How do Capacitors work?

Hi I am buuilding a car audio system and I was wondering if i add a capacitor that is only 2 farads to a 2000 watt Amp, will that actually hurt the performance or will it just not help as much as a bigger capacitor. What im trying to ask is even if the capacitor isn't sufficient alone, will it help marginally or would it have just been better to run traight from the battery?