In a large bowl or shallow dish, combine 1 can cola and 1/2 cup brown sugar. Add pork; turn to coat. Refrigerate 8 hours or overnight., Drain pork, discarding marinade. Place pork in a 5- or 6-qt. slow cooker. Add salt, garlic powder, onion powder, pepper and remaining can of cola. Cook, covered, on low until meat is tender, 8-10 hours., Set meat aside until cool enough to handle. Remove meat from bones; discard bones. Shred meat with 2 forks. Discard cooking juices and return meat to slow cooker. Stir in enchilada sauce, green chiles and remaining 1 cup brown sugar. Cook, covered, on low until heated through, about 2 hours., Serve pork in bowls over rice. If desired, add toppings.