Switched power supply conversion device capable of improving conversion efficiency and method

The invention discloses a switched power supply conversion device capable of improving conversion efficiency and a method. A direct-current power supply is enabled to be connected with a load through a power supply converter. The power supply converter is provided with more than one power switch. A first frequency is output by a pulse width modulation controller and is used for controlling the switching frequency of the power switch. A load current is detected by a current detector. A frequency conversion signal is produced by adding a judging condition and is sent to the pulse width modulation controller. The pulse width modulation controller is enabled to output a variable second frequency to adjust the switching frequency of the power switch. The judging condition is that the load is judged to be a light load or a heavy road according to the load current. When the load is the light load, the second frequency is reduced to reduce switching loss of the power switch. When the load is the heavy load, the secon