PowerShot G7 DC drive circuit from computer PSU

Hi, I'm trying to make Canon PowerShot 7G digital camera DC power brick so I don't have to buy one for 99$ out of computer PSU.

My camera has Li-ion battery pack NB-2LH 7.4V 720mAh.
It has 3 terminals plus and minus and third terminal don't know what it's for.

Is it possible to drive the camera using 12V from PSU stabilized using LM317T?

Do I need current stabilized circuit or voltage stabilized, or both?

Thanks.