The present invention discloses a method for controlling power supplies, each of M power supply has a first end and a second end, the first end of the ith power supply is connected to the second end of the (i−1)th power supply. The method comprises the following steps. A testing procedure is performed by each of the M power supplies for determining whether the first end and the second end are connected or not. A first connection status code is set when the testing procedure determines that the first end is connected, and the second end is not connected. A second connection status code is set when the testing procedure determines that the first end and the second end are both connected. A third connection status code is set when the testing procedure determines that the second end is connected, and the first end is not connected.