In a slow cooker, combine the chicken, bell peppers, pineapple, and onion.
In a separate bowl, whisk together the sugar, apple cider vinegar, ketchup, soy sauce, garlic powder, ground ginger, salt, and pepper until well combined. Pour this mixture over the chicken and vegetables in the slow cooker.
Cover and cook on low for 4 to 6 hours or on high for 2 to 3 hours, until the chicken is cooked through and tender.
In a small bowl, mix the cornstarch and water to create a slurry. Stir this into the slow cooker during the last 30 minutes of cooking to thicken the sauce.
Serve the sweet and sour chicken over cooked rice.