Add elbow macaroni, shredded cheese, chopped American cheese, butter, half and half, Dijon mustard, onion powder, salt, black pepper, and paprika to the slow cooker.
Cover the slow cooker and cook on Low for 2 hours, stirring every 30 minutes to ensure even cooking and to prevent the pasta from sticking to the bottom.
Once the pasta is fork-tender and the cheese has melted, the mac and cheese is done. If the pasta is still too firm, continue cooking for a bit longer.