I don't know if it's true or not, but some of the people involved in the show claim they've approached a physicist(?) about the reason for the blackout, and they said it was plausible.
It's sort of like when they say "Based on a true story" in a horror movie. Yes, some people really may have died in a house once, but it didn't have anything to do with ghosts or demons, it was just a straight up murder. They're trying to lend it an air of credibility, though.
Likewise, blackouts and EMP are quite real, but they behave nothing like the phenomenon in this series does. So, they get some expert who's willing to do a soundbite to say "Oh yes, EMP is quite plausible," and they lend the series an air of credibility even though the physics behind the final product has nothing to do with the general idea they mentioned to him or her initially.