A DC power supply including a DC voltage source, a converter for converting DC power outputted from the DC voltage source to AC power, a transformer for inputting the AC power outputted from the converter, a rectifier circuit for converting the AC power outputted from the transformer to DC power; a resonant circuit composed of a resonant switch and a resonant capacitor connected in parallel to a DC output side of the rectifier circuit; a filter reactor and a filter capacitor for smoothing the DC power outputted from the rectifier circuit, a snubber circuit connected in parallel to the filter capacitor, and a load connected in parallel to the filter capacitor, the DC power supply comprising: a first voltage sensor for detecting an output voltage of the DC voltage source; a second voltage sensor for detecting a voltage of the filter capacitor; a current sensor for detecting an input current or an output current of the transformer; and a controller for inputting output signals of the first voltage sensor, second voltage sensor, and current sensor, and outputting a signal that controls a gate pulse of a plurality of semiconductor devices (Q1-Q4) constituting the converter and a gate pulse of a semiconductor device (Qz) constituting the resonant switch and a signal that adjusts detection timings of the first voltage sensor, second voltage sensor, and current sensor; wherein the controller includes: first controlling means for adjusting supplied power by adjusting a gate pulse width of the semiconductor devices (Q1-Q4) of the converter in accordance with a sensor input while an operating frequency of the converter is maintained constant; and second controlling means for adjusting the supplied power by adjusting the operating frequency of the converter in accordance with the sensor input while the gate pulse width of the converter is maintained constant. a first voltage sensor for detecting an output voltage of the DC voltage source; a second voltage sensor for detecting a voltage of the filter capacitor; a current sensor for detecting an input current or an output current of the transformer; and a controller for inputting output signals of the first voltage sensor, second voltage sensor, and current sensor, and outputting a signal that controls a gate pulse of a plurality of semiconductor devices (Q1-Q4) constituting the converter and a gate pulse of a semiconductor device (Qz) constituting the resonant switch and a signal that adjusts detection timings of the first voltage sensor, second voltage sensor, and current sensor; wherein the controller includes: first controlling means for adjusting supplied power by adjusting a gate pulse width of the semiconductor devices (Q1-Q4) of the converter in accordance with a sensor input while an operating frequency of the converter is maintained constant; and second controlling means for adjusting the supplied power by adjusting the operating frequency of the converter in accordance with the sensor input while the gate pulse width of the converter is maintained constant. first controlling means for adjusting supplied power by adjusting a gate pulse width of the semiconductor devices (Q1-Q4) of the converter in accordance with a sensor input while an operating frequency of the converter is maintained constant; and second controlling means for adjusting the supplied power by adjusting the operating frequency of the converter in accordance with the sensor input while the gate pulse width of the converter is maintained constant.