To outsmart someone has the meaning of intentionally tricking someone or defeating someone using cleverness. Therefore, to outsmart oneself is to unwittingly catching oneself in one's own tricks. It's amusing when this happens, unless it happens to me. :P

“Outsmarting oneself” is a term used when; for example, someone accomplishes something that even impresses themselves. Perhaps I pass a test that I otherwise expected to fail or not do to well on but score 100%, I may say I outsmarted myself. Hope this helps.