That's a very pertinent question for me as well. I will ONLY use the IBM PS/2 style keyboard (the IBM Model M clicky type) and have one for each of my machines, even my work machine, plus a few spares in case one of these tanks ever fails.
I have adaptors to step the AT (large D) style connector down to the PS/2 size (small D) and I've got adaptors to plug PS/2 style mice into a USB port but I've never tried it with a keyboard.
Maybe it's time to do that. . .
I'm pretty sure that you'd have to use an AT or later keyboard since the original PC keyboards used a different interface. I don't think a PC would recognixe an AT keyboard and I don't think an AT can use a PC one.
Again, I haven't checked those and unfortunately the bulk of my collection is in storage for the time being.
Erik