It also depends on ig the amp is a regulated or non regulated design. Regulated means it makes about the sam amount of power even if the voltage drops and only draws a cretain amount even when making peak power. An unregulated amp usally tends to make more power but also draws more power to make it. If your amps are regulated its probably not that big of an issue to put a cap on it. Buy the amp first if you have problems with the electrical system lights dimming dead batt ect then you may need a cap.