A power supply system charging a battery of an electric car through a grid power line and supplying electric power stored in the battery to electrical equipment through an in-home wiring, including: an isolated converter connected to the grid power line, the in-home wiring and the battery; and a controller controlling the isolated converter. The isolated converter includes a plurality of isolated converter circuits each including two full-bridge circuits. One of the plurality of isolated converter circuits further includes two booster circuits. The controller receives load amount information depending on the operation state of the electrical equipment from a monitor device and switches, on the basis of the load amount information, an operating mode of the isolated converter to one of first mode to fourth mode. The controller causes the two booster circuits to perform a boosting operation in the first mode and third mode.