Saturn 2003 alternator

Whoever told you that doesn't know anything about electrical power. Your stock alternator is probably 100 amps which is 1200 watts of power. The stereo draws only a fraction of that so a bigger alternator will serve no purpose. Your stock alternator could run ten car stereos. Don't waste your time and money. Just check the >input< wattage or amperage of the stereo and you will see what I mean.

your stereo can be an issue if your headlights and or interior lights dim with the large hits from the subwoofer or your getting distortion. If this is the case just add a capacitor can or a stereo battery. No need to upgrade the alternator unless your using a 4000-watt amp or higher and the capacitor and second battery don't fix your problem.