A power supply device for a new energy automobile comprises a main power supply cable fixedly connected with a charging pile, a charging plug connected with the new energy automobile, and a telescopic part. The two ends of the telescopic part are provided with a primary power supply base and a secondary power supply base correspondingly. A sliding cavity extending leftwards and rightwards is formed in the telescopic part. A primary power supply groove and a secondary power supply groove are formed in the primary power supply base and the secondary power supply base correspondingly, and an opening of the primary power supply groove and an opening of the secondary power supply groove face the sliding cavity. Guide through grooves communicating with the sliding cavity are formed in the upper end wall and the lower end wall of the telescopic part correspondingly. A sliding joint head is installed in the sliding cavity in a left-right sliding mode. The sliding joint head is fixedly provided with guide plates in a vertically symmetrical mode. The guide plates stretch into the guide through grooves and are flush with the outer end walls of the telescopic part. A secondary power supply cable is fixedly arranged at the right end of the sliding joint head. The secondary power supply cable penetrates through a through hole formed in the secondary power supply base and is connected with the charging plug.