A power supply device and a power supply method in a data center, and the power supply device includes at least two busbars, where a first busbar of the two busbars is connected to a first battery, a second busbar of the two busbars is connected to a second battery, and a voltage level of the first battery is different from a voltage level of the second battery, and at least one first bidirectional direct current converter configured to connect the first busbar and the second busbar such that the first busbar and the second busbar perform electrical energy transmission using the first bidirectional direct current converter.