I have the Boss Metal Zone, but ever since I brought it to my friend's house, it has stopped working for me. The little red light will still be on, indicating that the batteries are still working, but it makes no sound, not even feedback. I still tried changing the batteries just in case, and that didn't work. It's not the wires because I can get sound from the amp when the pedal is turned off. I think it has to do with me putting in another adapter into the pedal that was not a Boss adapter, but I've used a universal adapter on it before and had no problems (besides the insane amounts of feedback). Is it possible that the other adapter could've "fried" my pedal? Or is there something else I'm not thinking about?

I've only had it for about half a year, and I heard reviews that complimented it's reliability, so I feel like I'm the only one who's had this problem.
Its entirely possible the adapter you used did fry it. Some pedals a little extra voltage isnt an issue, others a little extra is to much.