I mean, the external case for any sff psus, nearly like what seasonic did with their ATX titanium psus https://seasonic.com/prime-titanium-fanless, but still have space for a 92mm fan. The benefit for sandwich case is that air blown from bottom fans can't be block, it would go through the power supply and go up.
Now I get it.
Which dimensions or compatibility do you have in mind? A case like that would almost be as big as a standard Sfx power supply. Except the airflow, not many advantages here I can see.
Wouldn't my Sfx to meanwell bracket be enough already?