Power supply apparatus comprising: a first power device and a second power unit each adapted to be connected to a DC supply line (Wdc) to be connected to a load device and configured to supply DC power to said load device through the DC supply line (Wdc); load current measuring means configured to measure a current flowing through the DC supply line (Wdc) and output a measurement indicative of a magnitude of the measured current; judging means configured to, upon obtaining the measurement from said load current measuring means, judge whether or not the obtained measurement exceeds an optimal current magnitude; and controlling means, wherein said first power device is adapted to be connected to a commercial power source, and is configured to convert power obtained from the commercial power source to the DC power so as to perform constant voltage control of supplying a constant voltage to the DC supply line (Wdc) irrespective of a current supplied therefrom to the DC supply line (Wdc), the optimal current magnitude being defined as a magnitude of a current which is output to the DC supply line (Wdc) from said first power device operating its maximum power-conversion efficiency, said second power unit including at least one of second power devices, said second power device being configured to perform inclination control of monotonically decreasing an output voltage supplied therefrom to the DC supply line (Wdc) with an increase of an output current supplied therefrom to the DC supply line (Wdc), and of monotonically increasing the output voltage with a decrease of the output current, said controlling means being configured to, upon acknowledging that said judging means determines that the measurement exceeds the optimal current magnitude, send an instruction to said second power device such that a magnitude of the current supplied from said second power unit to the DC power line is identical to a difference between the measurement and the optimal current magnitude, said second power device including adjusting means configured to adjust the output current on the basis of the instruction received from said controlling means, and said adjusting means being configured to, upon receiving the instruction from said controlling means, modify a condition of the inclination control so as to adjust the output current to a current corresponding to the instruction without varying the output voltage. a first power device and a second power unit each adapted to be connected to a DC supply line (Wdc) to be connected to a load device and configured to supply DC power to said load device through the DC supply line (Wdc); load current measuring means configured to measure a current flowing through the DC supply line (Wdc) and output a measurement indicative of a magnitude of the measured current; judging means configured to, upon obtaining the measurement from said load current measuring means, judge whether or not the obtained measurement exceeds an optimal current magnitude; and controlling means, wherein said first power device is adapted to be connected to a commercial power source, and is configured to convert power obtained from the commercial power source to the DC power so as to perform constant voltage control of supplying a constant voltage to the DC supply line (Wdc) irrespective of a current supplied therefrom to the DC supply line (Wdc), the optimal current magnitude being defined as a magnitude of a current which is output to the DC supply line (Wdc) from said first power device operating its maximum power-conversion efficiency, said second power unit including at least one of second power devices, said second power device being configured to perform inclination control of monotonically decreasing an output voltage supplied therefrom to the DC supply line (Wdc) with an increase of an output current supplied therefrom to the DC supply line (Wdc), and of monotonically increasing the output voltage with a decrease of the output current, said controlling means being configured to, upon acknowledging that said judging means determines that the measurement exceeds the optimal current magnitude, send an instruction to said second power device such that a magnitude of the current supplied from said second power unit to the DC power line is identical to a difference between the measurement and the optimal current magnitude, said second power device including adjusting means configured to adjust the output current on the basis of the instruction received from said controlling means, and said adjusting means being configured to, upon receiving the instruction from said controlling means, modify a condition of the inclination control so as to adjust the output current to a current corresponding to the instruction without varying the output voltage.