A multipurpose power supply suitable for a power switch driver circuit takes an input voltage and generates output voltages at four output terminals. Two output terminals may be connected to voltage supply rails to drive a switched-mode power converter. The voltage output at each output terminal relative to ground is different, allowing the voltage rails to be set to voltages suitable for a variety of different power-switch driver circuits by adjusting the output terminals to which the voltage rails are connected. A reference voltage is applied to one output terminal in order to set the values of the voltages at the remaining output terminals.