From an I.T. management point of view, Delta are stupid.
Let's assume for a second that the whole outage was indeed caused by power circuits going down and backup power not kicking in. Fine, **** happens. Stuff fails.
What SHOULD have happened is that their entire system failed over to a backup SITE within 30 seconds. That is not impossible to do, and I just delivered a system (three months ago) that does just that. Ask yourself why Google, Facebook etc never go down. Redundancy, redundancy, redundancy and redundancy. And trust me, as an I.T. professional (MSc + JNCIE) I can guarantee you that this is not rocket science.
This time it's a power failure. Next time it's a criminal or terrorist act that takes out the entire DC.