In a 6‑quart slow cooker, add 1 1/2 cups grape jelly, 1 (12‑ounce) jar chili sauce, and 1/2 to 1 teaspoon cayenne pepper (use 1/2 tsp for milder heat or 1 tsp for hotter).
Stir the jelly, chili sauce, and cayenne together until the mixture is evenly combined and smooth.
Add 2 pounds frozen meatballs to the sauce and stir gently to coat all the meatballs.
Cover and cook on LOW for 4 hours, stirring once about halfway through to redistribute the sauce and meatballs.
After 4 hours, confirm the meatballs are heated through and the sauce is hot, then serve.