DC-DC actually converts DC to high freq. AC 1st, then uses a transformer and then rectifiers, smoothing, feedback, etc. If no isolation, i.e. common ground is fine, a choke instead of a transformer is fine too.
One possible benefit of a DC-DC circuit is that the converter can choose its switching frequency. That can give some room for optimizations for power or size.
So do AC-DC converters. They rectify the incoming AC, then it’s basically the same as a DC-DC converter. They have a switch that produces basically PWM in the hundreds of kHz to low MHz range, that it punches through a transformer.
