Abstract: A voltage boosting power supply, wherein a commercial power supply of 100 volt a.c., for example, is used as its primary power source, the input from the power source is accumulated in a capacitor and the accumulated power is then converted into a boosted a.c. power for delivery by means of an invertor, and which is provided with a storage battery as a preliminary power source for protection against power failure and arranged to disconnect the a.c. power supply from the capacitor and, instead, connect the battery across the capacitor through a high frequency switching element by switch means which operate in response to a power failure signal from a power failure detector. Accordingly, the output voltage of the battery is boosted by the capacitor and then applied to the invertor and, therefore, the output voltage can be raised without increase of the capacity of the battery and consequent increase in the size and weight of the device.