Can an adult son from a secret affair legally hold a DPOA over a spouse of many years? An unknown son appeared with a DPOA to oversee a person on life support. The family had idea this person existed. Doesn't the wife of 40+ here super cede this?

Who signed and issued the DPOA.

What county is this in, the US, England, Mexico, laws all differ

The wife should have no problem getting one of her own, and then the son can try to prove that he has more rights than she (and prove it's real). Sounds suspicious indeed without knowing who, if not the person on life support, issued it. He might want to prove he's the son while he's at it.