Toss potatoes and onion with flour in 6-quart slow cooker. Stir in stock, salt, garlic powder, pepper and thyme. Cover.
Cook 3 hours on HIGH or 6 hours on LOW.
Stir in ham, heavy cream and corn. Cover. Cook 15 minutes longer on HIGH or until soup is thickened.
Ladle soup into serving bowls. Garnish with chopped parsley, if desired.