wherein a current detection unit senses the voltage suitable for a power consuming device by modulat

An automatic voltage transforming power supply mainly comprises a wire set, a sensing and controlling unit, a switch unit and a transformation body. The wire set electrically connects the transformation body and a power consuming device, and the sensing and controlling unit senses the potential difference of the wire set. If the potential difference fits a predetermined voltage, the switch unit is activated to supply power to the power consuming device. The transformation body further comprises an output port, a voltage conversion unit, a current detection unit, and a selection control unit. The selection control unit controls the voltage conversion unit on a time sequence basis to modulate a plurality of different voltages which are outputted to the power consuming device via the output port; the current detection unit senses the voltage suitable for the power consuming device by modulation therewith and produces the current, and the selection control unit controls and fixes the voltage currently modulated b