Place the potato chunks into your slow cooker, add the onion and garlic powder and pour in the chicken stock. Cook on Low setting for 6-7 hours or High setting for 3-4 hours. You want the potatoes to be just soft enough to mash.
When the potatoes are cooked, right there in the slow cooker pot, mash the potatoes with a masher then stir in the butter, sour cream, parsley, cream cheese, and season with salt and pepper to your liking. Serve.