Combine the bacon, beef stock, cider vinegar, white vinegar, brown sugar, ketchup, red pepper flakes, chile powder and 1 tablespoon salt in a medium saucepan. Bring to a boil, then reduce the heat to medium low and simmer until the bacon renders its fat, about 15 minutes. Remove from the heat; set aside to let the flavors develop, 20 minutes. Remove the bacon. Reheat the sauce before serving.