The South Korean military has deliberately leaked information to reporters about plans to plunge its northern neighbor into man-made darkness. The plan called "Death Chain" is based on a massive strike on the territory of the DPRK with "blackout bomb" ammunition. They will not kill anyone (except indirectly), but they will cause a lot of problems for the northerners.
The graphite bomb contains no explosives. Basically, it is a container with a lot of carbon filaments. They are distinguished by their low weight, coupled with high electrical conductivity - if the ammunition is activated above the power plant, the territory will be covered by a "cobweb" of many wires. This will provoke a mass of short circuits with natural consequences for the equipment and the facility as a whole.
Graphite bombs can be used wherever there are electrical wires without insulation - in 1999, the United States tried to destroy Serbia's power grid with them. Without much success, but the risks of such strikes are small, especially for the civilian population. But there is a chance to leave the region without telephone communication, and in modern realities and without Internet access, which is very painful. It is only unclear to what extent this threat is relevant specifically for North Korea.
The South Korean military claims that they have fully studied the technologies for creating graphite bombs and can begin their mass production and use at any time. Only as a preventive measure, if they find the preparation of the northerners for war. Whether this will stop the very likely retaliatory strike from heavy artillery against multimillion-dollar Seoul is difficult to say.