A power supply system driving a load including a main power apparatus and a backup power apparatus is disclosed. The main power apparatus provides main power to the load according to city power. The backup power apparatus provides backup power to the load when the city power does not correspond to a first pre-determined condition and includes a recombination unit, a fuel cell unit, a transformation unit, and a control unit. The recombination unit recombines a methanol component to a hydrogen component. The fuel cell unit receives the hydrogen component to generate a first power. The transformation unit detects the city power and transforms the first power to generate the backup power. When the city power does not correspond to a first pre-determined condition, the control unit activates the reformer, the fuel cell unit, and the transformation unit to generate the backup power.