A nuclear plant in a war zone is a dirty bomb waiting to be set off, which is incredibly easy to do, technically. Gas and coal plants are also end up being easy targets, as the war in Ukraine has shown. The most reliable one is solar because of how distributed it is. You can knock off one solar field, but then there are rooftops. You really need to destroy a city if you want to get it rid of power completely.
(Diesel power generators also work, but they require constant fuel supply, which can be complicated in a war zone)
(Diesel power generators also work, but they require constant fuel supply, which can be complicated in a war zone)