Backup power supply and energy-saving method for the same to operate in cold redundancy mode

The invention discloses a backup power supply, comprising a main power line, a main power isolation unit, an auxiliary power line, an auxiliary power isolation unit and a microcontroller unit; the main power produces main power, the main power isolation unit receives and outputs the main power, the auxiliary power line produces auxiliary power, the auxiliary power isolation unit receives and outputs the auxiliary power, the microcontroller unit transmits a cold redundancy signal to the main power line and the auxiliary power line upon the receipt of the cold redundancy signal transmitted by an external system and transmits a first enable signal and a second enable signal respectively to the main power isolation unit and the auxiliary power isolation unit, the main power line and the auxiliary power line down-regulate the voltage levels of the main power supply and auxiliary power supply at the same time according to the cold redundancy signal, the main power isolation unit performs enabling according to the f