I am trying to figure out which one to buy, and have a question:

Do these cards require their own power source?

The reason I ask is that some of them come with a power adapter, and it looks like some of them have places to plug in an adapter. Why would this be the case, however? Does it matter what kind of computer you have, or whether you're using XP or not? None of the websites where I have been looking at them have been clear about this.

Thx for the help!