Were there any German POWs in the U.S.A. in either WW1 or 2?

Yes. It was better to have POW camps here because if they escaped, it would be harder for them to help out their allies. People with heavy German accents weren't trusted in the US during either war, so even if they escaped in the USA, they couldn't do much spying. And it would be next to impossible for them to get back across the Atlantic into Europe.