Multiple Power Girl Personality Disorder (MPGPD) is a serious and, currently, untreatable condition that happens when the character known as Power Girl has completely different personalities in the comics in which she appears. When Power Girl is taciturn in the pages of JSA or JSA: All Stars and a goofy bit of alright in the pages of her own self-titled (and, frankly, much more entertaining and engaging) comic you know you are witnessing a case of MPGPD.
How do you know this is happening? It’s simple: She looks the same but acts differently. She flies around, punches and takes down the bad guy and then cracks a joke that’s, actually, funny.