Embodiments of this application disclose a power supply apparatus, a power supply system, and a data center designed to reduce the number of power conversion steps, equipment costs, and circuit loss. The power supply apparatus includes: a solid-state transformer configured to convert an alternating current into a first direct current; a first direct current/direct current converter, coupled to the solid-state transformer and configured to convert the first direct current into a second direct current; an energy storage component, coupled to the first direct current/direct current converter and configured to perform energy storage on the second direct current; and a second direct current/direct current converter, coupled to the first direct current/direct current converter and configured to convert the second direct current into a third direct current, where the third direct current is used to supply power to a load.