A method and apparatus for providing uninterrupted DC and AC power for a desktop personal computer is described. The source of the uninterrrupted DC and AC power is derived from an integrated power supply that is sized to fit within the existing housings of most desktop personal computers as a plug-in replacement for existing power supplies. A high degree of efficiency is obtained using an integrated design with the main power conversion derived from a DC/DC dual primary resonant converter. The main primary of the resonant converter is driven from a high voltage DC bus which is supplied from AC mains when available. When the AC mains is unavailable, the second primary of the DC/DC dual primary resonant converter receives power from a low voltage battery source. Secondaries of the converter produce low voltage DC for driving the personal computer, high voltage DC for augmenting the high voltage DC bus, which in turn is used to drive a DC/AC inverter for supplying uninterrupted AC voltage for powering peripherals such as a monitor, printer, etc. A medium-voltage secondary is also sourced from the converter which drives a battery charger to recharge an internal battery pafck upon restoration of the AC mains.