I don’t know the answer, but I found this discussion which seems relevant.
https://electronics.stackexchange.com/questions/69666/atx-power-supply-front-end-how-does-this-work
The explanation given says it has to do with the functionality allowing the psu to be used with either 110VAC or 220VAC mains.
Does the psu you measured without input capacitance have a physical switch for selecting 110V or 220V?
Won’t someone think of the tech companies in these unprecedented times.
The focus should be on the widespread devastation to peoples lives. Who cares if the semiconductor industry has to deal with worse yields and higher prices? That’s not what matters right now.