To the basin of a 6-8 quart slow cooker, add the chicken stock, cubed potatoes, onion, salt & pepper, and cubed ham, reserving ½ cup of the ham for topping. Stir together. Cover and cook on LOW for 6 hours or HIGH for 4 hours, or until the potatoes are tender. Add in the evaporated milk, cubed cream cheese, and 1.5 cups of the shredded cheddar. Stir together, breaking apart some of the potatoes to thicken the soup. Replace cover and let cheeses melt. In a small skillet over medium high heat, add the reserved ham and pan fry until crisp. Serve soup topping with reserved cheese, bits of the fried ham, and scallions.