A power supply controlling device includes: a direct-current power supply configured to output a direct-current voltage; an alternating-current power supply configured to output one selected from between a superimposed voltage obtained by superimposing an alternating-current voltage onto the direct-current voltage and the direct-current voltage; a bypass capacitor configured to partially store therein an output from the alternating-current power supply and configured to, when the direct-current voltage is output from the direct-current power supply while no electric charge is stored therein, store therein a second direct current being a part of a first direct current output from the direct-current power supply in conjunction with the output of the direct-current voltage; and a power supply controlling unit configured to cause the direct-current power supply to control a level of the direct-current voltage based on a target value for the first direct current and a value indicating the second direct current.