A power enabling circuit for uninterrupted power supplies includes a main power supply system, a backup power supply system and a power enabling control circuit. The main power supply system is electrically connected to an external power source to convert and output a conversion power, and generates a first power good signal when the conversion power is output normally. The backup power supply system outputs a backup power when the main power supply system cannot output the conversion power. The power enabling control circuit receives the first power good signal output from the main power supply system and simulates to generate a corresponding second power good signal, and also includes a normal power supply state in which the second power good signal is sent to a motherboard and a backup power supply state to receive the backup power and continuously output the second power good signal to the motherboard.