Abstract: A voltage regulator capable of maintaining the output voltage of a unit, such as a power supply, incorporating said voltage regulator within, for example, .+-.5 percent of say, 115 volts, a.c., without any interruptions in the power supply output voltage and without any distortion of the a.c. sine wave.This is accomplished through the monitoring of varying secondary transformer output voltages according to the primary input voltage variations by means of a comparator processing a signal to power relays which switch to specific secondary transformer taps without causing interruptions of the output power and without distortions of the a.c. sine wave, respectively. Various additional devices are provided to enhance the described regulated a.c. power supply performance.