The 8 pin chip blew up. There was a sound like something shorted, chip had a black spot, and the light turned off.
What type of light, and how powerful?
Yes, I meant the LED light on the adapter itself.
Did it
came on and then "turned off" or did it stay off and was never on?
Reversing polarity should not light the LED at all and it would have stayed off from the start to finish. If it came on even for a brief moment then turned off, it was powered until the chip blew - which means it is unlikely you reversed the polarity. In this case, you have a short some where - possibly with your output actually drawing way too much current.
To ensure your board is properly powered, you need a DMM to measure exactly what you put into the spring (+) and negative of the board. In your picture, you have the red wire to the board labeled negative (-). Was that soldered by you or original? Visually trace the power wire and look for shorting. Use the DMM to check would help too. In the picture, it looks like the negative power wire is router by/around the USB plug, there could be a short there.
After you visually and DMM check for any shorts, if you are going to test it again without soldering, at least you electrical tape to insulate the exposed twisted "joint". It just could be the movement like pressing switch causing the exposed wire joint to touch something.
Silly as it sounds, look inside the plug to see if you have metal debris or wire fragments in there. After stripping the jacket from a wire, some times, small fragments of wire might have evaded proper disposal and it get caught by and then lodged inside the plug. I had such a wire fragment that got lodged on my ~2x3 inches small PCB but took me 1/2 hour to find.
Also, I hope you are not testing with the CLA in the car. The car can put out quite a lot of current. Do you have a power source to test it with? You need a 12V source with some kind of current limit. A current limiter is better than a fuse since a fuse will require replacement.
First, forget the switch and power to test the adapter directly without a switch by quick-touching the +wire to spring and the - wire to the negative. Hand holding the wire so you can disconnect quickly. Start with very low current like 5mA to 10mA, and gradually increase it until you see the LED turn on.
Once you get the setup to light the LED, you can increase current to the proper limit and test the output. When the output is right, only then it is the time to cut in and add the switch.