TECHNOLOGY FOCUS - ELECTRICAL POWER AND ENERGY - Preferred Device: In the power supply device, the electric storage device is connected to the first line and the second line; and the fuel cell stack is connected to the second line and the third line. A drive circuit, driving at least one of a first pump supplying reactive gas to the fuel cell stack and a second pump supplying refrigerant to the fuel cell stack, is connected to the first line and the second line or is connected to the first line and the third line. The electric storage device is connected to the first line and the second line, the fuel cell stack is connected to the second line and the third line, a drive circuit, driving at least one of a first pump supplying reactive gas to the fuel cell stack and a second pump supplying refrigerant to the fuel cell stack, is connected to the second line and the third line. The first DC-DC converter is a chopper type comprising choke coils (32); and the choke coils are common mode coil. Additionally, the first DC-DC converter includes a three-phase bridge circuit (31) in which a switching element is bridge-connected, and a three-phase choke coil as choke coils; a core of the common mode coil is a rectangular core; any one-phase choke coil of the three-phase choke coil is dispersed and wrapped around one pair of opposite sides among two pairs of opposing sides included in the rectangular core; and a two-phase choke coil of the three-phase choke coil, excluding the one-phase choke coil, is respectively concentrated and wrapped around another pair of opposite sides among the two pairs of opposing sides included in the rectangular core. Electric power is supplied to a load from the first line and the third line, the power supply device further comprising: a power consumption obtaining unit, obtaining a power consumption of the load; a target electric power distribution setting unit, setting a target electric power distribution of the fuel cell stack and the electric storage device, based on the power consumption; and a duty control unit, controlling a switching duty of the first DC-DC converter so that an actual electric power distribution of the fuel cell stack and the electric storage device equals the target electric power distribution. The power consumption obtaining unit obtains the power consumption, the power consumption including an external load power consumption of an external load of the power supply device and an internal load power consumption of an internal load of the power supply device. The power supply device also comprises a target electric current setting unit, setting a target electric current of the fuel cell stack or the electric storage device according to the target electric power distribution, where the duty control unit performs a feedback control of the switching duty so that an actual electric current of the fuel cell stack or the electric storage device equals the target electric current. It further comprises a target electric voltage setting unit, setting a target electric voltage of the fuel cell stack or the electric storage device according to the target electric power distribution, where the duty control unit performs a feedback control of the switching duty so that an actual electric voltage of the fuel cell stack or the electric storage device equals the target electric voltage. The target electric power distribution setting unit sets a target output ratio of the fuel cell stack and the electric storage device as the target electric power distribution; and the duty control unit performs a feedback control of the switching duty so that an actual output ratio of the fuel cell stack and the electric storage device equals the target output ratio. The power supply device also comprises an electric motor that drives a vehicle, the electric motor being supplied with electric power from the battery circuit; a target setting unit, setting a target output electric current or a target output electric power of the fuel cell stack as zero or a positive value; a detection unit, detecting an output electric current or an output electric voltage of the fuel cell stack; and a duty control unit, performing a feedback control a switching duty of the first DC-DC converter, so that the output electric current detected by the detection unit equals the target output electric current, or the output electric voltage detected by the detection unit equals the target output electric voltage; where the duty control unit continues the feedback control during a regenerative operation of the electric motor that drives a vehicle; and electric power is supplied from the first line and the third line to a load. The target setting unit sets the target output electric current or the target output electric power to zero during the regenerative operation of the electric motor that drives a vehicle. Preferred System: The power supply system further comprises vehicle auxiliary machinery, where at least one part of the vehicle auxiliary machinery is connected to the first line and the second line or is connected to the second line and the third line, or is connected to the first line and the third line. The at least one part of the vehicle auxiliary machinery is connected to the power supply device through the second DC-DC converter. The at least one part of the vehicle auxiliary machinery includes an air conditioner.