A power supply system having a plurality of local systems that each have an AC line to which a plurality of power consumers are connected, a power storage device, and a local inverter device that connects the power storage device and the AC line, and having a linking inverter device that connects the power storage device of one local system and the AC line of another local system between the local systems such that the plurality of local systems are electrically connected in series, the power supply system comprising: an interrupting device capable of switching the AC line of one local system among the plurality of local systems and an external power system that is separate from the plurality of local systems to one of a connected state and a parallel-off state in which the AC line of one local system is paralleled off from the external power system; and a control device capable of controlling operation of the local inverter devices, the linking inverter device, and the interrupting device, wherein when the AC line of the local system that can be connected to the external power system via the interrupting device and the external power system are in the parallel-off state, the control device causes the local inverter device of each of the plurality of local systems to operate in a parallel-off operation mode in which control is performed such that the voltage of power on the AC line is at a target voltage and such that the frequency of power on the AC line is at a target frequency determined according to the state of charge of the power storage device, wherein, if the control device determines that a condition for switching to the connected state has been satisfied, with respect to the local system that can be connected to the external power system via the interrupting device, the control device stops operation of the local inverter device in the parallel-off operation mode and establishes the connected state by operating the interrupting device, and thereafter causes the local inverter device to operate in a charging operation mode used in charging the power storage device with supplementary power received from the external power system, and wherein the control device determines that the condition for switching to the connected state has been satisfied if a set time is reached, or if the state of charge of the power storage device of the local system that can be connected to the external power system via the interrupting device is less than a lower limit state of charge. an interrupting device capable of switching the AC line of one local system among the plurality of local systems and an external power system that is separate from the plurality of local systems to one of a connected state and a parallel-off state in which the AC line of one local system is paralleled off from the external power system; and a control device capable of controlling operation of the local inverter devices, the linking inverter device, and the interrupting device, wherein when the AC line of the local system that can be connected to the external power system via the interrupting device and the external power system are in the parallel-off state, the control device causes the local inverter device of each of the plurality of local systems to operate in a parallel-off operation mode in which control is performed such that the voltage of power on the AC line is at a target voltage and such that the frequency of power on the AC line is at a target frequency determined according to the state of charge of the power storage device, wherein, if the control device determines that a condition for switching to the connected state has been satisfied, with respect to the local system that can be connected to the external power system via the interrupting device, the control device stops operation of the local inverter device in the parallel-off operation mode and establishes the connected state by operating the interrupting device, and thereafter causes the local inverter device to operate in a charging operation mode used in charging the power storage device with supplementary power received from the external power system, and wherein the control device determines that the condition for switching to the connected state has been satisfied if a set time is reached, or if the state of charge of the power storage device of the local system that can be connected to the external power system via the interrupting device is less than a lower limit state of charge.