Venezuela shows the way. Big cities cannot exist without electricity. Cut their power. Conductive wires shot over major power lines to ground them out would do it. Hard to patrol whole power lines that go for miles through the forests, fields and deserts.
I recall studying the effects of Y2K in the event it actually happened. Big cities would be toast, period. Like you said, a power outage and they are gone.
Many do not realize the dependence city water, sewer and gas depends on electricity. Standby generators have enough fuel for typical emergencies such as storms. Not for long term.
Sewage, lack of food and medical care would kill many. Low lying areas would back up raw sewage into homes (no lift stations to pump it up hill). This would create a cross connection to whatever freshwater would be left, thus contaminating water with sewage.
Then the armed gangs and other’s turning into looters.
The list of things lost would include refrigeration, gasoline, food stores, and of course no one could buy a gun or ammo.
Literally speaking, it would not be a dog eat dog scenario, it would be a people eat dog, a dog eat people scenario.