Not sure if trolling or genuine concern. Assuming goodwill, cyber-attacks cannot cripple power grid. Power grid core components are either mostly analog, manually operated, or within the intranet (no access to the internet).
Cyberwarfare is overrated and portrayed as an omnipotent power where a nerdy-looking college kid can somehow take down an entire government by slamming his fingers on a small laptop.
Cyberwarfare is slow and oftentimes its just denial of service (you cannot access what you want because millions of bots are overloading it). You often need massive computation powers and hours of time to break through a system. Even after if you can break into a system, most you can do is copy/steal information.
Defacing/destroying/disabling a system is often just not possible, and even if it is, it's quite reversible.
TLDR - We can deal with cyber attacks. Our cyber-warfare (mostly freelancers, few groups work with govt. occasionally) is among the best in the world,.