There was a massive blackout over a large part of Canada and some of the states in 2003. Since it was awhile ago, I don't remember the technical details of how and why, but if you Google "Blackout 2003" you'd probably find the answers to most of your questions.

Oh, but I do remember that my particular area was without power for approximately... 16 hours. Other areas went more than 24 hours.

Also having worked in a couple of different retail stores during blackouts, I can also tell you that most of them will have backup generators for lights, but that's it.