Click on the three dots to the upper right of your post.
Thanks, I should have known. Anytime you see three of anything at the upper right, click on it just to see what happens.
That's one of the things I like about RetroPie on the Raspberry Pi. You can use just about any controller you like, and it automatically converts the old control inputs to what you have, and if you don't like their conversion you can change it. I mainly use an SNES like controller, as the latest games I have are SNES games. A lot of people use PS3 type controllers. I have both wired and Bluetooth, with the latter being my favorite, as I'm not tied to the machine by a cable. Still, the controller that came with the case I got is very similar to the original SNES controllers, both in feel and build quality. It only came with one, and you couldn't buy a second one, but a couple of months ago they started selling them separately. Much better than the "2 for $14.99" junk, of which I have a set.