Obviously, but not all. I can't believe I have to say this, but prolonged blackouts (with all the downstream ramifications they bring to hygiene, temperature control, food safety, food availability, etc) would cause infant mortality to exponentially rise as days pass without power.
I would disagree. The dark ages were hundreds of years ago, the electric grid is much less than a century old. Plenty of countries have unreliable supply and rolling blackouts and have adapted to it or have just never became accustomed to the luxury of 24/7 electricity on demand. Being without juice is not the end of the world.
Those places generally have the luxury of 24/7 electricity, normally via diesel gensets, for key parts of their infrastructure, such as fuel transfer, hospital, food supply.
The places that don't have the fallback ready access to fallback diesel genset, like rural South Sudan or Burundi, are pretty close to an end of the world scenario.
Don't romanticise disaster. If a developed country indefinitely lost power, a huge swathe of the population would die, starting with the infants, elderly, and chronically ill. Then hunger and disease would come for the rest. Nonsense ideas that we'd MacGyver or bushcraft our way out of trouble are infantile.
Without the power grid we are right back to the dark ages in a matter of a few days. Except at least in the dark ages people sort of knew how to survive. Now, only a minority of people really know how to survive without modern conveniences.