POWER SUPPLY SYSTEM AND POWER SUPPLY DEVICE

A power source system (1) has a power supply recipient (20) that operates by consuming power from a main power source (30) of a vehicle, and a power source device (10) that backs up power supply to the power supply recipient (20). Upon recognizing that a power switch (31) of the vehicle has been turned off, the power supply recipient (20) generates a stoppage permission signal (S2). The power source device (10) determines that an abnormality has occurred in a power source line (L2), on which the power switch (31) is provided, of a power supply path (L1 to L8) between the main power source (30) and the power supply recipient (20), when a first determination condition, a second determination condition, and a third determination condition are all met. The first determination condition is that voltage (V1) on the power source line (I2) is lower than a voltage threshold value (V1th). The second determination condition is that the power source device (10) has not received the stoppage permission signal (S2). The third determination condition is that a communication state between the power source device (10) and the power supply recipient (20) is normal.