Can you imagine living in NYC without electricity? Back to the 1800s w the flick of a switch.
No.
Vastly worse than the 1800s, at the flick of a switch.
In the 1800s, the population density was much smaller for the simple reason that the buildings were not as tall. They were designed for life without electricity. Today's buildings are unlivable without electricity. The NYC water distribution system is dependent upon electricity. Transportation (gas/diesel pumps) are dependent upon electricity; there aren't enough horses in the entire USA to replace NYC engine powered transportation. Food preservation is entirely dependent upon electricity; food preparation largely so.
Cut off power to NYC, and zombies will flood the countryside.