A power supply apparatus includes a plurality of power modules for receiving alternating current power to provide the power to a load; an uninterruptible supply module to supply self-power to the load; an inverter module installed on one side of the power modules or the uninterruptible supply module to convert the power and provide converted power to the load; direct current bus bars provided inside enclosures of the power modules, the uninterruptible supply module, and the inverter module, respectively; and a connection bus bar for connecting adjacent direct current bus bars, wherein in the power modules and the uninterruptible supply module, an alternating current/direct current converter or a direct current/direct current converter is provided in the upper portion of the direct current bus bar, or the alternating current/direct current converter or the direct current/direct current converter is provided in the lower portion of the direct current bus bar.