The SaV64 is an over-voltage protection device for Commodore 8-Bit computers that require both 5VDC and 9VAC power sources. It monitors the 5VDC voItage level and automatically disconnects both the AC and DC from the computer when it rises above the trip voltage.

Note - This manual is from 2017 and came with batch 4 of this product.  Future versions may be different.

Lemon64 forum thread 

YouTube video