Power supply system for electric vehicle and control method thereof

A power supply system for electric vehicle and a control method thereof are provided, the system including a high voltage battery (110) formed with a plurality of battery cells and generating a power driving source to a motor of the electric vehicle, and a low voltage battery (120) generating a power driving source for electrical load (150), and an On-Board-Charger (OBC) selectively charging a high voltage battery (110) or a low voltage battery (120) using an externally-supplied AC power source (OUTSIDE AC POWER) based on an output voltage level of the low voltage battery (120).