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In video above, they use same system as you suggested. Only they have used isolation transformer.
In my opinion that schematic have high ripple and relatively large capacitance on output. So short...

You are right, I just put low percent from top of my head. Anyway is still sub 1uS.
Just came to my mind, If you have linear output stage, lowest SMPS voltage could be much higher, eg 40V. In that...

That is first example that I found to get theory of operation for phase shifted forward smps. You calculate your transformer for maximum voltage that you need on output, with lowest voltage on input....

You didn't mention nothing about ripple, resolution, off line or main referenced, earth referenced, isolated...
I would go with offline full bridge phase shifted forward smps with linear output...