IF there is an EMP
10% will not even notice that it happened.

But, an "EMP" is more of a hoax than an actual threat.
So, you take a nuke, focus it into the EM spectrum (instead of into heat and force) annnddd, you might black out a city and its suburbs. Maybe.

It is all highly theoretical. Maybe the military has actually practiced.
But i doubt it because it doesn't actually work well with actual physics.

So, my guess is that the "EMP" will be some guy at the electric station turning on/off/on/off the power and that will fry a bunch of people's stuff