To economically improve the reliability of a duplexed power supply which converts an alternating-current voltage into a direct-current voltage and supplies it to a load.

This power supply is provided with power supply terminal boards 1A, 1B, which are connected with alternating-current power supplies in different systems through distribution lines 6A, 6B and have power switches 4A, 4B and power supply boards 2A, 2B which contain alternating current-to- direct current converting parts 5A, 5B for converting an alternating-current voltage into a direct-current voltage to be supplied to a load. The output terminals on the power supply terminal boards 1A, 1B and the input terminals on the power supply boards 2A, 2B are connected with each other through connection wires 7, 8, in such a manner that the boards in the same systems are connected with each other. Furthermore, the output terminals on the power supply terminal boards 1A, 1B and the input terminals on the power supply boards 2A, 2B are cross-connected with each other through connection wires 9, 10 such that the boards in the different systems are connected in parallel with each other.