I have a 250gig internal HD in my PC that I use to back up all my pics, files, and videos. I'd like to make this an external so I can use it with my tablet. I know its just a matter of getting a case. What I want to know is will it work with out an external power source. It seems pointless if I have to have a powered HD. Eliminates the portability of the tab. I saw one on newegg for $10 that does not have an AC adaptor and another for $20 that has an AC adaptor.