I have a 1991 F-150 XLT Lariat 5.0Lefi 2wd. I put a stereo in my truck and my subwoofer amp fried my alternator twice due to too much draw, so i put in a couple stereo capacitors. Now when i drive the alternator moves closer to the fender liner compared to where it usually is close the the block. Belt squeeks and reads at the N in normal on voltage gauge the sometimes stops squeeling and gauge goes back to the M in normal. Why?

 

Capacitors can be used to filter /smooth out power fluctuations. They don't do anything to increase power output. If you go to a larger output alternator you might consider a dual belt drive set-up.