The same power that the datacenters need to run off of? Brilliant move! If somehow it targets power that hurts a lot of people without killing itself, that would not impede a citizen with a backhoe from cutting the fiber to the datacenter. Humans could restart power generation pretty quickly after that.

You make several bad assumptions. First, the AI could be in another location that would not be affected by the power outage. If it's operating off self-preservation, that would be a given. If it's working on behalf of a foreign power, it might be local and affected, but the damage would already be done. Which brings me to point two, why do you think you would be able to get the power back up and running? A Stuxnet type attack could make plants inoperable for months.