Ok well I searched ALLL over and though I'm sure I read about it somewhere I couldn't find it, so I have decided to post what I found along with a diagram of what I found. :-)
This is for a Dell Latitude D800 Laptop Power Supply Brick (and I'm 'assuming' all the other laptops that this brick and similar support).
Basically there are 3 wires coming from the brick to the laptop. It was easy enough to figure out the +19.5vdc and the GND, but the third wire... wasn't sure if it was needed and if all hell would break loose if not connected or whatever...
So... here's the diagram
The Power Supply Type Wire IS NOT NEEDED, but when you power on the laptop, the BIOS will say that it can't tell what power supply is connected. Just say you know and you don't want to be bothered by the prompts again. You're golden ;-) Hope this helps.