A system includes a generator configured to be coupled to a power input of an uninterruptible power supply (UPS), an engine, a hydraulic motor and a mechanical coupling mechanism configured to selectively couple the engine and the hydraulic motor to the generator. The system further includes a hydraulic accumulator and a valve configured to fluidically couple the hydraulic accumulator to the hydraulic motor. A control circuit is configured to control the valve, the mechanical coupling mechanism and the engine in conjunction with the UPS to supply power to the UPS.