A power supply system comprising: a vehicle; and a power feeding device (200, 300) for receiving power from said vehicle and feeding the received power to a load external to said vehicle, said load being configured to receive power supplied from an external power supply and be driven thereby and to also receive power from said vehicle and be driven thereby once said external power supply has failed, said power feeding device (200, 300) including a communication unit (240, 350) for communication between said vehicle and said power feeding device (200, 300), and a power supply unit for supplying said communication unit (240, 350) with power, said vehicle including a power generation unit (100, 135), a power feeding unit for receiving power from said power generation unit (100, 135) and supplying the received power to said power feeding device (200, 300), and a control device for controlling said power feeding unit to convert the power received from said power generation unit (100, 135) into power to drive said load following a predetermined specification when said external power supply has failed, when said external power supply has failed, said power feeding device (200, 300) is configured to supply the power that is received from said vehicle to said power supply unit to activate said communication unit (240, 350), characterized in that: when said external power supply has failed, said power feeding device (200, 300) is also configured to transmit via said communication unit (240, 350) to said control device a specification regarding power supplied from said external power supply to said load, and once said specification regarding power supplied from said external power supply to said load has been received, said control device is configured to follow said specification regarding power supplied from said external power supply to said load, rather than said predetermined specification, to control said power feeding unit. a vehicle; and a power feeding device (200, 300) for receiving power from said vehicle and feeding the received power to a load external to said vehicle, said load being configured to receive power supplied from an external power supply and be driven thereby and to also receive power from said vehicle and be driven thereby once said external power supply has failed, said power feeding device (200, 300) including a communication unit (240, 350) for communication between said vehicle and said power feeding device (200, 300), and a power supply unit for supplying said communication unit (240, 350) with power, said vehicle including a power generation unit (100, 135), a power feeding unit for receiving power from said power generation unit (100, 135) and supplying the received power to said power feeding device (200, 300), and a control device for controlling said power feeding unit to convert the power received from said power generation unit (100, 135) into power to drive said load following a predetermined specification when said external power supply has failed, when said external power supply has failed, said power feeding device (200, 300) is configured to supply the power that is received from said vehicle to said power supply unit to activate said communication unit (240, 350), characterized in that: when said external power supply has failed, said power feeding device (200, 300) is also configured to transmit via said communication unit (240, 350) to said control device a specification regarding power supplied from said external power supply to said load, and once said specification regarding power supplied from said external power supply to said load has been received, said control device is configured to follow said specification regarding power supplied from said external power supply to said load, rather than said predetermined specification, to control said power feeding unit. a communication unit (240, 350) for communication between said vehicle and said power feeding device (200, 300), and a power supply unit for supplying said communication unit (240, 350) with power, a power generation unit (100, 135), a power feeding unit for receiving power from said power generation unit (100, 135) and supplying the received power to said power feeding device (200, 300), and a control device for controlling said power feeding unit to convert the power received from said power generation unit (100, 135) into power to drive said load following a predetermined specification when said external power supply has failed, when said external power supply has failed, said power feeding device (200, 300) is also configured to transmit via said communication unit (240, 350) to said control device a specification regarding power supplied from said external power supply to said load, and once said specification regarding power supplied from said external power supply to said load has been received, said control device is configured to follow said specification regarding power supplied from said external power supply to said load, rather than said predetermined specification, to control said power feeding unit.