Abstract: A battery-less uninterruptable sequel power supply that converts mechanical rotation generated by a local power source to electrical power in the event of commercial line power distortion or failure is provided. The uninterruptable sequel power supply uses a voltage and frequency-tolerant rectifier-inverter combination that converts the decaying output of a de-accelerating synchronous alternating current machine to a stable alternating current voltage for driving a critical load. In the arrangement of the invention, there is no need to maintain rotary velocity of the synchronous alternating current machine during the transitory period between fault detection and connection of a prime mover.