Mix dry cake and pudding mixes in large bowl with whisk until blended.
Add next 4 ingredients; mix well. Stir in chopped chocolate.
Pour into slow cooker lined with foil and sprayed with cooking spray; cover with lid.
Cook on LOW 4 to 5 hours (or on HIGH 3 to 3-1/2 hours) or until top surface of cake has no wet spots and cake begins to pull away from side of slow cooker.