My non-scientific observation is that folks 1. Panic 2. Buy a generator, any generator, 3. Start it up 4. plug things into it until they don't work.

The hardest thing for folks to understand is the need for "surge" power. When things with electric motors start, they demand more current then when running. Sump pumps and refrigerators/freezers are the most common, but some medical devices may also be in this category. You need a generator with the power to handle the "surge" demands as these motors start up.

When I was still using a portable gennie, I was able to keep the fridge and freezer cold enough by simply running one at a time for 4-5 hours, getting cooled down, then switching to the other. Usually (YMMV) a fridge or freezer can hold food at a safe temp for that length of time.