Brown the ground beef and diced onion in a skillet over medium heat for about 6 to 8 minutes, stirring and breaking the beef into crumbles, until the beef is no longer pink and the onion is softened.

Drain excess fat from the skillet, then transfer the cooked beef and onion to a 5- to 6-quart slow cooker.

Add the taco seasoning, ranch dressing seasoning, black beans, pinto beans, kidney beans, corn, diced tomatoes, tomatoes with green chiles, tomato sauce, and 1 cup of broth. Stir well, adding the second cup of broth if you prefer a thinner soup.

Cover and cook on LOW for 6 to 8 hours or on HIGH for 3 to 4 hours.

Stir before serving and adjust the consistency with additional broth if necessary. Taste only after cooking before deciding whether any extra salt is needed.

Ladle into bowls and serve with shredded cheddar or Mexican-blend cheese, sour cream, diced avocado, sliced green onions, cilantro, tortilla chips, or lime wedges.