A power supply device having variable output voltage includes a controller, and a first power supply module and a second power supply module connected in parallel. The controller selectively outputs a first voltage control signal and a first switch control signal to the first power supply module, or outputs a second voltage control signal and a second switch control signal to the second power supply module according to a voltage requirement signal. An output power of the first power supply module has a first voltage value selected from a first voltage value set, an output power of the second power supply module has a second voltage value selected from a second voltage value set, and a minimum value of the first voltage value set is greater than a maximum value of the second voltage value set. Thus, more extensive voltage output capabilities are provided, and good power conversion efficiency is achieved at the same time.