A power supply apparatus of an electric car and a method of controlling the same. The power supply apparatus includes a small power generation unit including a plurality of small generators mounted on an axle shaft of wheels of the electric car, to which a main drive motor is not provided, and each generating allocated resupply power preset in association with rotation of the axle shaft; a charging unit including a battery mounted in a trunk of the electric car, the charging unit charging the battery with the power generated by the small power generation unit and supplying power for operation of electric and electronic circuits of the electric car and power for the main drive motor; and a controller having a function of treating an abnormal state of the small generators and controlling overall operation of the power supply apparatus.