A board includes a functional module, and further includes n switch modules, where first ends of the n switch modules are connected to the functional module, and second ends of the n switch modules are connected to n main power interface units respectively, where n is an integer greater than or equal to 2; and a power supply selecting module connected to control ends of the n switch modules, where the power supply selecting module is configured to detect residual power of the n main power interface units, select, from main power interface units with residual power greater than or equal to rated power of the board, a main power interface unit with lowest residual power as a power supply interface unit, and control a switch module connected to the power supply interface unit to be switched on.