Vehicle power-source device and control method for vehicle power-source device

A vehicle power-source device comprising:

• a capacitor configured to store regenerative power that is output from an alternator;
• a DC/DC converter having a voltage conversion part configured to convert an output voltage of the alternator and supply the converted voltage to a main battery and a load group;
• a first current sensor configured to detect discharge current of the capacitor at a time of a regeneration operation;
• a second current sensor configured to detect charge current that is supplied to the main battery from the DC/DC converter;
• and
• a control part configured to decrease an output voltage of the voltage conversion part to a level at which the charge current is not supplied to the main battery, by decreasing an output voltage setting value to be supplied to the voltage conversion part, when both a discharge current detection signal that is produced when output power of the alternator decreases to less than output power of the DC/DC converter during the regeneration operation of the alternator and that is output from the first current sensor and a charge current detection signal that is output from the second current sensor are received during the regeneration operation of the alternator.