Stuff about power adapter in regards to the OP
Without even reading the thread after the first post, I was gonna suggest the power adapter as the problem. Those cheap 3-in-1 adapters available these days are pure junk. There's a couple of different ones out there, and they all suck. The one from Retro-bit is especially garbage. The only useful thing about them is being able to get the SNES plug because I can't find it for sale anywhere.
MagOps, like others have suggested, I recommend getting an official power adapter. Finding them for not too much money can be kinda tricky though. As of this post, there's a few on eBay as low as $14.99 with a best offer option. Not too bad.
Although I do like to point out this other option: You can find any power adapter with the correct specs (10v 850mA but I'm sure you can use a 9v adapter just fine) to use, as long as it isn't shit. Normally this isn't an option with the US SNES because it uses that wacky plug, but you have the shitty 3-in-1 that you could use. You'd just have to splice it on. You can find power adapters in thrifts stores for super cheap (usually a few bucks a piece).
Personally, that's what I would do. I would cut the SNES plug off that 3-in-1 and splice it onto another adapter that's useable. Then after that, the 3-in-1 isn't completely garbage. I was able to use one on my Famicom without any problems, but not my Genesis.
