Adafruit 2.1mm DC Barrel Jack to 1st Generation MagSafe Adapter [ADA3546]
If you've ever owned a 1st generation MacBook, you'll recognize this little friend. The premise of this 2.1mm DC Barrel Jack to 1st Generation MagSafe Adapter is simple. There's a MagSafe plug on one end and a 5.5mm/2.1mm DC barrel jack with center positive polarity on the other. This allows you to connect a 15-20VDC power supply to something that expects to connect to 1st gen. MagSafe.
Since you can easily destroy hardware using this adapter, we really recommend it only for experts and people who fully understand what they're getting into by pushing arbitrary voltages into their fancy computers! Use a multimeter to probe the magjack pins to verify you've got the right voltages before plugging in into your computer.
There is no regulator or voltage protection in this adapter. If you plug in an incorrect power supply or wire it backwards, you could destroy your laptop - so be really careful!