How important is a stable power grid with respect to being at war? Would a power grid that is taken down cripple our ability to fight?

Per Sergio Caltagirone, Director of Threat Intelligence at Dragos (a cybersecurity firm) "If you take down a country's electrical grid you're probably setting yourself p for an act of war".

So hostile foreign power X destroys our power grids (Russia maybe). How does that affect us if we are at war? No dispatching drones remotely? What else?