Place chicken in a 4- or 5-qt. slow cooker. In a small bowl, mix sugar, soy sauce, vinegar, garlic, ginger and pepper; pour over chicken. Cook, covered, on low 4-5 hours or until chicken is tender., Remove chicken to a serving platter; keep warm. Transfer cooking juices to a small saucepan; skim fat. Bring cooking juices to a boil. In a small bowl, mix cornstarch and cold water until smooth; stir into cooking juices. Return to a boil; cook and stir 1-2 minutes or until thickened. Serve with chicken and, if desired, rice.