Switching power supply device

A switched-mode power supply device provided with a plurality of power supply circuits that correspond to phases of a polyphase alternator, the switched-mode power supply device comprising:

• a switching circuit that allows switching of a phase connected to one of the plurality of power supply circuits not corresponding to a certain phase of the polyphase alternator, the switching being done between the certain phase and a phase to which the power supply circuit corresponds;
• an inrush current prevention circuit that is disposed on a power supply line on a negative electrode side of the polyphase alternator and is disposed at a position closer to the polyphase alternator than a connection point at which the plurality of power supply circuits are connected is to the polyphase alternator, the inrush current prevention circuit being configured to prevent an inrush current;
• and
• a filter circuit disposed at a position closer to the polyphase alternator than the switching circuit and the inrush current prevention circuit are to the polyphase alternator, the filter circuit being a circuit in which all lines for the phases are magnetically coupled to one another.