A power supply device including: a transformer generating, from an input voltage, low output voltage and high output voltage; an upper limiter circuit receiving the high output voltage and controlling the high output voltage not to exceed a maximum; a power controller performing feedback control on the input voltage so that the low output voltage matches a target voltage; an operation mode acquirer configured to acquire an operation mode of an image forming device; and a target value controller configured to change the target voltage depending upon the acquired operation mode. The target voltage when consumption amount of current with the high output voltage is relatively great ensures that the high output voltage does not fall below a minimum of a rated voltage range of the high output voltage, and is higher than the target voltage when consumption amount of current with the high output voltage is relatively small.