An uninterruptible power supply has first and second input terminals, first and second inductors, first and second AC switch units, first and second storing devices and a control unit. The first and the second inductors are electrically connected to the first and the second input terminals. The first and the second AC switch units are electrically connected to the first and the second inductors for conducting input currents. The control unit is electrically connected to the first and the second AC switch units which may be turned on and off thereby to control the first and the second inductors which charge the input currents and discharge the input currents to the first and the second storing devices.