Mix stock, garlic powder, sea salt and black pepper in 6-quart slow cooker until well blended. Add potatoes and onion.
Cook 8 hours on LOW or 4 hours on HIGH or until potatoes are tender.
Mash potatoes slightly with a potato masher until desired texture. Stir in heavy cream, sour cream and 1 cup of the shredded cheese. Cover. Cook an additional 15 minutes on HIGH or until desired thickness. Sprinkle with bacon, green onions and remaining ½ cup shredded cheese before serving.
