FRAM/Champ makes them, well most of the popular ones last I heard. Not all are e-core type, as I still see the "classic" design around. Wife's Buick 3.6L uses an AC PF64 which has steel tube and end caps. That's a suuuuuper popular engine, too.
AC Delco is GM's brand that GM sells to dealerships, so they buy a lot of stuff from a lot of different suppliers and slap their name on it. The GM dealerships service non-GM cars, too, so they buy filters/plugs/belts/etc for all those cars too and simply put the AC Delco name on it.