From CBS News:
About two hours after the game, officials revealed that an "abnormality" in the power system triggered an automatic shutdown, forcing backup systems to kick in. But they weren't sure what caused the initial problem.
New Orleans Mayor Mitch Landrieu called the power outage "an unfortunate moment in what has been an otherwise shining Super Bowl week for the city of New Orleans."
Sounds like they really nailed the cause there.
Oh well, at least because of the blackout we got to see the Go Daddy kiss commercial one more time.