A power supply system providing backup power comprises at least one power supply, at least one power storage unit and a power integration panel. The power supply converts an input power into a conversion power and sends at the same time a power good signal to a motherboard. The power storage unit receives the conversion power in normal conditions and saves electric energy to generate a backup power. The power integration panel includes a power control unit connected to the power supply to determine whether the conversion power is output through the power good signal, a backup control unit connected to the power storage unit to compare the conversion power and backup power to determine whether the backup power is output, and a power regulation unit connected to the power control unit and backup control unit to regulate the conversion power or backup power to be an output power.