What is the preferred method of connecting a new foundation (footing and stem wall) to an existing foundation?

Drill holes in old concrete and put a 12" piece of #4 rebar in it with expanding epoxy -- or is there a better way?

What requirements have any of you had to meet in the past with such an add-on?

That's the exact method that our structural engineer usually recommends for the architectural firm that I work for. Do not under cut the existing structure. Don't make any excavation that invades a 45 degree slope from existing bearing surface.