VEHICLE POWER SUPPLY SYSTEM

A vehicle power supply system includes a main power supply system including a main low-voltage power supply and a normal load; and a backup power supply system including a backup low-voltage power supply and an emergency important load. The backup power supply system includes a backup power supply control device. The backup power supply control device executes a suppliable electrical energy estimation process of estimating suppliable electrical energy suppliable from the backup low-voltage power supply to the emergency important load. The backup power supply control device outputs a signal based on a first electrical energy threshold value and a second electrical energy threshold value.