A power supply having a stable reset function a mobile electronic unit is provided that simultaneously resets the digital signal processing unit and the controller in a mobile electronic unit. The stable reset function occurs during the period of time when the power source of the mobile electronic unit is changed by removing an AC adapter from the mobile electronic unit and applying the power source of the battery which was previously installed in the mobile electronic unit. The power supply having a stable reset function includes a power supply unit, a first reset unit, which, when at least one output voltage from the power supply unit is abnormal, generates a first reset signal, a second reset unit, which, when the input power source from the adapter or battery is less than a predetermined reference voltage, generates a first reset signal, and a controller which is reset by means of one of the first and second reset signals, and when the second reset signal is applied thereto, controls the power supply unit to cut off the source voltages for the digital signal processing unit.