Coat a 5-quart electric slow cooker with cooking spray. Combine berries, orange juice, and sugar in slow cooker. Cover and cook on HIGH for 2 hours.
Combine cornstarch and water in a small bowl, stirring until smooth. Stir cornstarch mixture into berry mixture. Cover and cook on HIGH for 15 minutes or until sauce thickens. Serve compote over angel food cake.
Ingredient Tip: If you only have one or two types of berries, you can still make this compote. Just make sure the berries add up to a total of 6 cups.