Hey, thanks for trying to help! I appreciate it : )I'm going to suggest something but maybe do not try it unless you hear from TiberiumFusion himself first, because I have a feeling that my method might be a bit overkill.
Open up Windows Explorer, and in its address bar, try typing %AppData%\Terraria Tweaker 2 . This should land you in TT2's config files, which I believe do not get uninstalled when you uninstall TT2 (though I may be wrong with this, since I only ever used the standalone version). So if these got messed up during the power cut, it maybe your saving grace.
Anyway, in this directory, take all items except the Tweak Lists folder (so you keep your tweak lists intact, which should be what basically matters for you), and move all those items somewhere else. Deleting them would have the same effect, since the point is to make TT2 not see them anymore, but then it'd be a pain or nigh-impossible to get them back, if something goes wrong.
So once that's done, the only remaining item in this directory should be Tweak Lists.
At this point, you could reinstall TT2 again, and then run it, and see if it changes anything.
Lastly, though you did say that you tried to reinstall Terraria, you could try verifying its files just in case (it'll take no more than a few seconds, usually), mainly to make sure that the executable is vanilla. The XNA redist files shouldn't have any issues either.
Good luck, dude.
Unfortunately, upon simply running the uninstall.exe for TT2, that didn't fix things for me. So after re and un installing again (to double check I guess?), I did pretty much what you suggested; I deleted the entire TT2 folder and everything in it (after backing up my tweak list elsewhere).
So (as far as I can know, being only a half step above tech-illiterate) I should have everything for TT2 fresh, new, and pristine.
Didn't work : (
So I tried to Verify Terraria via Steam, and it said 1 file needed to be redownloaded. Did that, yet every time I try this, it still fails to verify afterward, and says 1 file is going to be redownloaded. Uninstalled and completely removed Terraria (all files/saves) from my computer, again hoping a "totally clean" install would fix it somehow. Thank goodness that Terraria is such a lightweight game to download.
Nope, same results. 1 file always fails, and redownloads. Even after fresh install. TT2 still has same error process. :' (
I should note, launching vanilla Terraria via Steam works without any issue. Not sure what the deal is.