One of the very best people I've ever hired wore a dark navy 3-piece suit with pristine french cuffs and gold cufflinks, if I remember correctly. The team almost dinged him for that, if not for his amazing technical talent, problem solving skills and eidetic memory.
A friend of mine used to where a suit for exams. He said it helped him get in the right mindset.
It probably helped him to feel in the right way for an interview.