A power supply apparatus

The power supply is disclosed. The device is a transformer which transforms the voltage on the power supplied from the power switch, the switch controller, the power switch for controlling the power switch for switching the power supply, the output is connected to the secondary side of the transformer circuit and the output from the output circuit in the power supply apparatus having a feedback circuit for feeding back a voltage, in response to a control signal, and varying the voltage output from the output circuit, having an output voltage variable circuit for applying a variable output voltage to the feedback circuit and that is characterized. Therefore, according to the present invention, through observation of the variable resistor of the voltage that is output from the output circuit of the power supply, and, it can easily vary the output power by the conversion.