My understanding is the EMP going off at high altitude around long cable creates a high voltage spike, destroying transformers at substations. Similar to running a magnet by a loop of wire to create electricity. Anything with a long wire (electrical grid) is going to be more vulnerable than tiny microcontrollers such as in a car with short wires. The equipment at substations is typically custom built and connected to these long wires so they will be destroyed and most substations don't keep equipment reserves. So think about the difficulties of trying to replace critical and custom substation equipment when fuel pumps don't work and substation equipment manufacturing plants don't work.  Also, who's going to put in the long term labor to try and build the custom equipment and transport it to the substations when their families are starving to death? It's not just Hollywood. I feel sorry for anyone that thinks their bubble of safety is invincible and as such don't care to prepare.