power (but don't expect the alternator to last very long). For cases where the alternator and capacitor are properly sized it really doesn't make any sense. Yes a capacitor will have resistance and act as a parasitic load (since its series compared to the battery in parallel) but theres no reason a modern alternator shouldn't be able to provide enough power for even the biggest sound systems if done right. The capacitor is designed to stabilize the voltage swings that occur from the alternators voltage regulator trying to compensate for the big changes in current draw, it should only have a minimal effect on total available power.
That said-you know your stuff and I've certainly heard the claim other places so I can't dispute that. Just wouldn't get my vote as being factual.