Power supply cooperation system and uninterruptible power supply device

A UPS device is coupled to an external power source and another UPS device through a power line. The UPS device includes: a storage battery in which power from the external power source is charged, the UPS device being configured to be capable of supplying power charged in the first storage battery to the power line coupled to the UPS device; a communication unit that communicates with the another UPS device through the power line; and a determination unit that determines whether the power line is in normal condition or not based on whether a communication between the UPS device and the another UPS device has been successfully established or not. Power is supplied from the storage battery to the power line that has been determined to be in normal condition by the determination unit.