Combine the jellied cranberry sauce, chili sauce, brown sugar, garlic powder, and black pepper in a large skillet or saucepan. Heat over medium heat, stirring occasionally, until the sauce is uniform and hot, about 5 minutes.
Add the frozen meatballs directly into the sauce and stir so each meatball is coated well. Lower the heat to medium-low, cover the pan, and let everything simmer gently for 15 to 20 minutes, allowing the meatballs to heat through.
Once heated, move the meatballs and sauce to a serving dish or keep warm in a slow cooker set to warm. Optionally, sprinkle with chopped parsley or rosemary before serving to add a fresh touch.