With the 49ers down by 22 and Colin Kaepernick having just been sacked, the Superdome power outage couldn't have come at a worse time.  The lights remained out for 34 minutes, and did seem to cause a serious momentum shift in the game which allowed Sand Francisco to come within inches of winning the Super Bowl.  If the 49ers had won, this Super Bowl game would forever have been tainted with the "what if" factor, as many would've pondered whether or not they would've been able to see victory without the help of the power outage.  

During the power outage, the NOFD (fire department) was called to the stadium due to the smell of gas being detected and also to free various people who were trapped in an elevator; however, the FBI released a statement denying that a fire had started.  Entergy, the power company responsible for powering the Super Bowl, and SMG, the company that manages the Superdome, provided a vague explanation as to what caused the power outage:

"Shortly after the beginning of the second half of the Super Bowl in the Mercedes-Benz Superdome, a piece of equipment that is designed to monitor electrical load sensed an abnormality in the system. Once the issue was detected, the sensing equipment operated as designed and opened a breaker, causing power to be partially cut to the Superdome in order to isolate the issue. Backup generators kicked in immediately as designed."

After the devastation of hurricane Katrina, the Superdome was revamped with an entirely new electrical power system, all paid for by FEMA.  However, it wasn't enough as there were various signs dating as far back as September 2012 that the power available for the stadium wouldn't be enough to handle the Super Bowl. There were various modifications made to increase the power capacity within the Entergy electrical services and systems at the Superdome, all which were priced in the high six figure range, on multiple occasions all the way up to December.

A lot of people debated whether or not Beyonce's electrifying halftime show caused a surge in the stadium's power which made the lights go out, but that theory was debunked.  In the end it's been implied that officials who are in charge of the Superdome knew in advance that the power system they had set up wouldn't be enough to handle the big night.

Further details will arise eventually regarding the power outage.

Source: deadspin.com