A fuel cell block (3), which has become highly resistive due to a defect and which is connected in series to other fuel cell blocks (3) in a direct-current power supply device (1), impedes the flow of current from the other fuel cell blocks (3). This results in a drop in output of the direct-current power supply device (1). In order to solve for this problem, the invention provides that a power diode (7) is connected in parallel to each fuel cell block (3). This power diode causes the current from the other fuel cell blocks (3) to bypass the defective fuel cell block (3).