S Korea is far more advanced and dependent on electronics for their basic economy. An EMP attack by the US would likely hurt our ally S Korea more than our enemy N Korea.
The sub aspect is interesting but, I think, irrelevant.
That is true. We could use “soft bombs” to attack NK’s power grid. Instead of an explosive blast or an EMP pulse,soft bombs (BLU-114/U) spread out carbon fiber filaments to short out a power grid.