second_stooge said: I'm lost, I know I don't read the comics, but I thought that they were the same person/kryptonian. Can someone explain?
one is a older version of the other from a alternate Earth, one in which she landed on Earth as a full grown adult, with a much much mature/developed body... The Kryptonian names are also spelled different, with Power Girl being Kara Zor-L, and Supergirl being Kara Zor-El. Power Girl joined the JSA on her Earth and was the Chairman of the JSA on the shared Earth her and Supergirl came to live on. Power Girl also adopted the name Karen Starr.
