Is there a certain kind that I need? Does it have to be Canon brand? How much do these cost? If I get one of these, does that mean I can just plug it into the electrical outlet and use the electricity power? I'm assuming that's what a power adapter is. I just don't want to end up buying the wrong thing. A power adapter connects your camera to the electrical socket just like any other power device.
Your Canon S2 User manual says that you should use the...
"Compact Power Adapter CA-PS700"
It's on page 171 of the camera user guide.
I'm not sure if you have to use the Canon brand...you probably could use another brand as long as the power specs are the same. You should perhaps ask a major camera retailer, who might be able to help you with a compatible AC adapter.
Anyway, page 171 of the manual gives you the specs. you get the adapter together with the packages | 