In fact, the PWM circuit has already shouldered the work of voltage rectification. The input voltage will be corrected again before passing through the switch, and the voltage entering the transformer has become a square wave. Therefore, the waveform output by the transformer is also a square wave, not a sine wave. Since the waveform is already a square wave at this time, the voltage can be easily converted into a DC voltage by the transformer.
That is, after the voltage is re-corrected by the transformer, the output voltage has become a DC voltage. This is why switching power supplies are often referred to as DC-DC converters.