I found this out from another post, not a clear answer but it could be right. Tehres a quote and a link to the thread.
"I believe the alternator is rated at about 105 amps I believe, it may be more, but that's pretty close. Apparently, I'm not making a clear enough point, a more powerful alternator is only going to charge the battery quicker, it won't stop your system from putting excessive load on the battery. Since the battery is charged by the alternator. Caps, aren't that problematic, the charge just as quickly as the discharge when in the system. That's the nature of it. Most common circuits only require small capacitors to handle power fluctuations. Your computer for example probably has less than a full farad through all the picofarad capacitors inside it. It just frustrates me that anytime someone says "my lights dim" that someone else says, you need to buy a hopped up alternator, when that just simply isn't the case. Most of the people in here aren't running enough power to ever utilize the alternators extra capacity. Yeah if you are running, 4-6 subs and over 2500+ Watts then I can see the need, but I've seen much more than what I have run on much less without caps. I have no dimming problem with a 650W RMS amp, and I have NO DIMMING, none, with the ac on screech, the lights on, 4 ways flashing, rear defroster and all interior lights. It doesn't get much more extreme than that, and I have NO DIMMING. I have the STOCK battery, I have the STOCK alternator. I am running 4 gauge power wire, with a clean 4 gauge ground. Even with the stereo up to 25 on the stock head unit, and a bass disc in the deck, I get NO DIMMING, ( I do get a headache though ) I have no cap. Unless you are gonna start some serious power consumption with your system, then you shouldn't have to upgrade your ALTERNATOR of all things, the battery maybe, or add a cap, an alternator won't change the dimming, your battery will still run down just as it did with the old one, the only difference will be how long it takes for it to charge up again."
It's 1/2 of the way down on the second page on my computer.