Heat a few tablespoons of oil in a large Dutch oven or skillet over medium heat.
Add the onions and jalapeño and cook until soft. Add the garlic, chili powder, cumin, and sugar and cook for about a minute.
Add the tomatoes, tomato sauce, and stock. Season with salt and pepper.
Bring to a simmer, then transfer to the bowl of a slow cooker.
Add the corn, beans, and chicken to a 5-quart (or larger) slow cooker. Cover and set on low for 6 to 7 hours (or high for 4 hours).
Give the soup a taste and season the soup with additional salt, pepper, and cayenne pepper, if needed.
Serve with cheddar cheese, sour cream, tortilla chips, and cilantro.
