I too am descended from a Mingo (Jenkins) who was from South Carolina. I have come across several possible meanings for the name Mingo. The first derivation that I came across was as you stated a form of Mandingo. Mingo was a common name among the Wolof and also Hausa. The next was Native American. The Mingo people were a part of the Iroquois nation in the Northeastern U.S. and the name was also used as a given name. This is probably not likely to be the source of the name in my family though. The other alternative is that it could be of Spanish origin, a shortened form of Domingo. This might be a possibility as well since my Mingo may have origins in Beaufort, SC on Santa Elena (St Helena) which was a Spanish settlement first. I am leaning toward the African origins.