The present invention presents an uninterruptible power supply device including an input circuit coupled between a voltage input terminal and a rectifier circuit, in which the input circuit includes a boost choke being charged with an AC current received from the voltage input terminal for providing a boosted AC voltage to the rectifier circuit. The rectifier circuit is configured to convert the boosted AC voltage into an intermediate DC voltage. The intermediate DC voltage is converted through an inverter into a poly-phase output AC voltage for use by a load.