POWER SUPPLY APPARATUS

The power supply apparatus a main power device, an auxiliary power unit, and controlling means. Each of the main power device and the auxiliary power unit is configured to supply DC power to a DC supply line. The main power device is configured to generate DC power by use of power supplied from a secondary cell. The controlling means is configured to, when a measurement (a magnitude of a current flowing through the DC supply line) exceeds an optimal current magnitude, send an instruction to the main power device such that a current supplied from the main power device to the DC supply line has the same magnitude as the optimal current magnitude. The optimal current magnitude is defined as a magnitude of a current supplied to the DC supply line from the main power device operating so as to maximize a proportion of power supplied from the main power device to the DC supply line to the sum of power supplied from the secondary cell to the main power device and loss caused by an internal resistance of the secondary cell. The main power device is configured to adjust the magnitude of the current supplied to the DC supply line on the basis of the instruction received from the controlling means.