I've been buying the old fashioned peanut butter for years. 2 tips: first, turn the jar upside down before opening and the oil will filter up through the peanut butter. Open it before it settles at the other end and you won't have to do much stirring. If that doesn't work, I dump it into a plastic container that is about twice as big as the jar. I use a butter knife to stir it up; doesn't take much time and it's less mess than getting anything electric involved. Once stirred, store in the refrigerator and it won't separate again.
I buy Adams old fashioned and unsalted so it's nothing but peanuts. I find the commercial ones (Skippy, Jif etc) to be absolutely awful with the salt, sugar, chemical stabilizers; you can't even taste the peanuts. Somebody recently gave me a jar they couldn't use at the end of a vacation and I ended up throwing it out.
Sue