The Yemeni power network is small and unreliable to start with. I met several Yemeni soldiers while contracting and generators are a big market there because the central power grid is junk.
I don't know anything about power grids and how much they scale, but I'm not sure an attack on Yemen's power grid holds any real lessons on how a larger and more robust system could be attacked. Perhaps some of our resident electricians could help out.
Here's an article to give you an idea of how fragile and small the system we're talking about is: Yemen | Electricity | GlobalPost
There have been many attempts over the years at attacking our power grid, most are unsuccessful at least on a large scale. The problem is that if they take down a large on like in NY it affects a lot more than just that area. And there are simple fixes that cost very little that could protect the grip from attacks, as well as solar storms. I doubt we'll do it though, we'd rather close down coal plants and hike up rates.