@Narasimham I'm guessing that you mean 'Tablet PCs where Tablet is used as an adjective'. OP does not mention the reverse string. But if you take time to look at 'noun adjuncts', 'attributive nouns' here, you will see that in say football manager, all linguists regard the pre-modifier football as still being a noun rather than an adjective.
– Edwin AshworthJul 30 '20 at 13:16
@Mick Some people say "PC" is a collective noun... Some people say that "PCs" are not very formal.
– user393388Jul 30 '20 at 13:24
Like in Asprin tablets.. we state its content at first. may also conform to the grammar of the language of a non-English speaker.
– NarasimhamJul 30 '20 at 13:25
I would use tablet PCs. Life's too short to worry about such things.
– MickJul 30 '20 at 13:39
@Narasimham it is also "desktop PCs" and "laptop PCs". The personal computer is not a medicine, so "PC desktops" and "PC laptops" does not sound right.
– Weather VaneJul 30 '20 at 13:39
I do not believe that anyone says that PCs, a most technical term, is not formal. I do not believe that anyone uses PC as a collective noun. And I do not for a minute believe that they would be mistaken for a native speaker if they did.
– RegDwigнtJul 30 '20 at 13:55