How much voltage does an alternator put out?

Automotive Alternator Output Voltages

With a properly operating alternator, AND electrical system, a voltage output range of 13.5 Volts to 16 Volts is considered acceptable.

Just the alternator puts out around 120 vac, but most newer alternators include a built in rectifier that limits voltage output to between 13.5 and 15.5 volts DC depending on speed.