Cook ground beef and yellow onion in a large skillet over medium heat until browned, stirring to break up with a wooden spoon, about 8 minutes; drain fat.
Transfer beef mixture to a 4- to 5-quart slow cooker. Add beef broth, potatoes, tomatoes, soup, tomato sauce, ketchup, and mustard. Stir to combine.
Cover and cook on Low 9 to 10 hours or on High 4 ½ to 5 hours, until potatoes are tender.
Stir Cheddar cheese into the soup.
Garnish servings with pickles, red onion, additional cheese, ketchup and mustard.