An uninterruptible power supply (UPS system) includes a first converter circuit, a second converter circuit and a DC bus coupled to the first and second converter circuits. The system further includes a control circuit configured to control the first and second converter circuits and to selectively couple the first and second converter circuits to an AC source and a load to provide a first mode of operation wherein the first and second converter circuits respectively operate as a rectifier and an inverter to serve the load from the AC source and a second mode of operation wherein the first and second converter circuits operate as parallel inverters to serve the load from the DC bus. The control circuit may be configured to couple the AC source to the load to bypass the first and second converter circuits in a third mode of operation.