It's definitely not a requirement for all countries. I am aware of Albania and some of the FSU countries, like Georgia, as places where it is a requirement. Edit: I've just checked the Georgia site and they now say it "will be useful" where as before it was required. Maybe double check with your consulate, though the link I posted had a recent update date on it.
And there is no clear statement of what you need re a public charge, as it is so individual. It depends both on your assets and if they think you will be able to find a job, etc. So a younger person with hardly any savings but a decent education in a sought-after field might be ok, as an example. Although I also see lots of people from poorer countries not get asked any proof of finances at all and still get visas...