I did a quick search and was surprised to not find any posts about these. If there was one I missed and this is a repeat post, my bad. Apparently they were put up on youtube years ago by a guy named Eric Draven under the username KatyPerrylolol, but have since been removed from his channel and reuploaded here and there by others.
Even with how crappy some of them sound, I still just really enjoy them and it makes me wish for an acoustic album like this. I even like how the original vocal tracks sound with the acoustic tracks.