Photos and Screenshots: https://imgur.com/gallery/bpmJglE
By the way, I used a screenshot that was originally from this post: Have I bricked my Arduino Uno? Problems with uploading to board
I was trying to wire two TEC1-12706 Peltier plates to my breadboard, and I saw that using the USB connection for power was not enough for both plates. So, I found a 19v--3.9A DC/AC adapter/computer charger and plugged it in to my Uno via the Power Jack port. The Peltier plates were not wired to the board when I plugged it in and everything looked fine, all the normal LEDs on the UNO lit up, etc. Then, I wired a peltier plate to my breadboard. As soon as I did, a part exploded, and grey smoke come out of the "L" light area. I unplugged it immediately. The next day, I plugged the adapter back into the Power Jack port and a screenshot is attached of some observations I made by touching the board. Photos of my Uno are also attached. As you can see, the "Slightly less hot but still burning part" is pretty much destroyed. The "L" light will not light up and as of right now I can't upload any code to it. Might be an unrelated issue so I will continue troubleshooting that, but it is still another observation. The test LED I wired is lit up, so I guess the board can still kinda function? I'm high school student and obviously a complete beginner. Will continue to do research on this. I really want to know what happened. Please help? Thanks everyone.