Can I strip a half inch of wire from a #8 cable and screw directly into a 38660 Molex connector? Or do I need to buy a spade terminal. This is for an AC connection to the back of a DC power supply, there are not clear instructions on the data sheet. https://www.molex.com/pdm_docs/sd/386608802_sd.pdf
That part you linked specifically says it has a captive plate. This is a plate which looks like a square washer with ridges in it that is wide enough to reach all the way to the walls on either side of the screw. It is used to give the screw a wide area to clamp down onto the bare end of wire and to ensure that all wire strands are clamped and secure no matter how far the they splay out when you tighten the screw. This second part is really important and the main reason why you really shouldn't just use a plain screw to tighten down a wire.
Your particular model has slightly curved plate to match the round contour of the wire. That's what that little curved piece of metal is is under the screw in the photo. The curved nature of your captive plate (which I have never seen before) makes it so your block actually works better with a bare end of a wire and not so well with a terminal connector. Usually they are flat so work equally well either way.
In cases where you have no plate, you can get away with adding a large washer, but it's not as reliable since the washer's chord (in the mathematical sense for circles) near the walls edge is so small that there is almost no material to contain the loose wire strands. Even less reliable is no washer and I never recommend that since at least half your wire strands will end up splaying out and be loose. But if you're in that scenario then you might as well just use a ring or forked/spade terminal instead.
Molex’s Beau barrier strips provide a wide variety of screw, terminal and mounting options, fitting a multitude of applications. Barrier strips accept either bare or terminated wires. A full complement of solder tabs, jumpers and quick connects is also available. Molex can provide solutions in either board-mounted or feed-through wire-to-wire styles.
Terminal blocks like this are built for spade terminals (what you call forks). I'm sure with some work a wire could be wrapped around the terminal, don't do this if you can help it).
If you don't use a spade terminal on the wire, you would need to back the screw all the way out of the block wrap the wire around it, then insert it back into the block.
Use a spade terminal, crimpers and spades can be found at most any hardware store, or automotive store.
If you don't use a spade, you might want to consider a clamping terminal block that is built for connecting directly to wires.