A controllable power supply device with a step-up function including a constant voltage generator, a programmable voltage generator, a first switch and a linear regulator is provided. The constant voltage generator is used to provide an initial voltage. The programmable voltage generator is used to receive the initial voltage and adjust the received initial voltage to boost the initial voltage to a power supply voltage. The first connecting terminal of the first switch is used to receive the initial voltage, the second connecting terminal of the first switch is used to receive the power supply voltage, and the third connecting terminal of the first switch is coupled to one of the first connecting terminal and the second connecting terminal. Therefore, the voltage from the third connecting terminal of the first switch is stabilized and is outputted as the output voltage of the controllable power supply device by the linear regulator.