I've actually just started my Dreamcast collection.
I've since picked up a Dreamcast (obviously), 2 official controllers (the white ones), an AV cable (as they gave me an RF adapter with my system, lol), A keyboard and mouse (dreamcast mouse and innovation keyboard, both of which I haven't quite figured out how to test), MSR, Hydro Thunder (which I got a refund for since it was scratched to hell and DOA), Dreamkey 2.0, PSO V2, Alien Front Online and Crazy Taxi (which were also both covered in scratches and DOA). Thankfully, AFO *did* come with the little mic adapter though.
I also picked up 2 after market controllers, as honestly, the official ones are a bit too small for my hands.
I have a blue "Performance" controller, which is *gigantic*. I find it's much like the (original) original XBOX controller, which my household lovingly refers to as the "hamburger controller", as it looks like a large, sloppy hamburger.
I've also grabbed 2 of the "High Frequency" controllers. They are by FAR my favorite controllers for the console, at least in my limited experience. However, they seem fraught with problems. The first one was perfect except for an X button that just didn't work. The second one has even weirder issues. Some buttons don't work at all, and others activate all kinds of buttons they shouldn't be. I've been using a controller test ROM I burned to see what the buttons do. For example, when I press right on the dpad, nothing happens. But when I press left on the dpad, left, down, right, A, B, X, Y, *and* the right trigger all light up on the diagram onscreen. I have none of the technical knowledge to fix it, and it's very distressing as I think it's the most comfortable controller I'll get for the Dreamcast.
Would anybody know where I could go to either get help in repairing it, or who I could send it to, to have it fixed?