The stock charging system on all the XS650's 70 through all years is a 3 phase alternator. The earlier years, 70-79, used a mechanical regulator with a separate selenium rectifier. The later 80 up used a solid state combined reg/rec.
Depending on your bikes year depend on which system it has.
On our 650's the regulator controls the alternator output to about 14.5 volts. The rectifier changes the 3 phase AC current to DC current.
Leo