Of course it's annoying, but the idea that you can schedule maintenance in a way to avoid this is also pretty ridiculous. Things break. Are you suggesting that Delta was negligent in some way that caused this??
It's certainly possible. It seems like testing the power, especially before a long-haul, would be a very easy step. For all we know, the power was not working because a circuit was tripped, or someone forgot to turn something back on during a regular check. It could very well be negligence or human error of some kind, and on a brand new plane, it probably is.