If you see any problems, I will never be too proud to make any necessary adjustments
Step 1: What You Need
1. Standard 110 standard US home outlet (don't know if it will work in other countries)
2. 12V home plug
3. Car adapter (12V)
4. Multi-tool (wire stripper, crimper, etc.)
(Optional) A car plug "cup" adapter
Step 2: What You Do
Take the wire from the 12V adapter, and cut the wire just before the end of the cord (where you plug it into something).
Next strip the covering off enough wire to connect it to the car adapter.
(Note: the end contact will always work, but only one of the side contacts works (usually)
I connected the positive to the end contact and the negative to the side contact.
NOTE: You can also buy a car adapter cup, (positive for the middle, negative for the outside contacts) for clean reuse, less resistance, and less strain on the devices. Then clean-up everything with electrical tape or shrink wrap. (the importance brought to my attention by LasVegas)
This method Extremely encouraged for those with any heart problems.