A power supply apparatus and method for providing electric energy to a target system are provided. The power supply apparatus includes: a capacitor module configured to store electric charge and provide electric energy to a target system based on the stored electric charge; an internal battery module configured to be operably connected with the capacitor module in series; and an output interface configured to couple the internal battery module with the capacitor module. The internal battery module and the capacitor module provide electric energy to the target system in controllable series connection through the output interface.