Pour broth into large pot. Add chicken. Bring to boil, reduce heat and simmer until chicken is tender. Remove chicken, reserving broth, drain chicken and let cool enough to handle; then shred or dice. Keep broth on low burner.
While chicken cools, add onion, pepper, serrano, garlic to blender. Add water to cover, process until vegetables are pureed. You can do more or less; I like to leave just a little texture to them. Add this to reserved broth. Increase heat to simmer. Add cumin to broth.
Remove about a cup of the hot broth to a saucepan. On low heat add cheeses and stir continuously until smooth. Add more broth if necessary. I actually add hot broth to the cheese in the blender and pulse gently, but this requires extreme caution to avoid getting burned. When smooth and homogenous, add to hot broth in original pot.
Add Rotel. Add chicken to pot. Heat through, simmer a few minutes to blend flavors and cheese into the soup. Just before serving, add chopped fresh cilantro, salt and pepper if desired and adjust seasonings to taste. Place handful of chips in each bowl, ladle soup over chips, garnish as desired with more cilantro, diced onion, more peppers, sour cream, avocado, anything you like, and enjoy!