Combine ketchup, brown sugar, honey, garlic, chile-garlic sauce, soy sauce, and five-spice powder together in a bowl. Let sauce stand at room temperature for 1 hour.
Add frozen meatballs to a slow cooker. Pour sauce over meatballs and toss gently to coat.
Cook on Low for 4 hours, stirring occasionally.
Notes
You can adjust the heat level by adding more or less chili sauce.