A power device with a protection circuit is provided. The power device includes a power module, a power output terminal, a converter module, a bus capacitor, and a protection circuit. The power module receives an input power. The converter module, the protection circuit, and the bus capacitor is electrically connected between the power module and the power output terminal. The protection circuit is configured for overvoltage protection when the input power being overvoltage, suppressing the surge current when booting up the power device, and regulating the voltage on the bus capacitor under overvoltage and undervoltage conditions.