Alternator question

I would think you had a weak charging system before stereo install. Most modern electronics need full 12 volts to operate. The light bulbs etc.., OEM to your car will function with low voltage, just pizz poorly. Assuming you still have the OEM gauge, does that needle twitch with turn signal operation? There's your sign.
If you have a voltage drop to regulator and alternators field ( that blue wire ), a higher amp alternator and/or different regulator wouldn't cure anything. Correct what you have first. Then if a higher output alternator is needed, it will work as it should.
@67Dart273 is better at diagnose/troubleshoot charging system than I.