Brown the beef in a skillet over medium-high heat, breaking it into small crumbles; drain well and season with chili powder, cumin and salt.
Transfer the beef to a 4-quart slow cooker and add the American cheese, cheddar, evaporated milk, tomatoes and jalapeƱos.
Cover and cook on low for 60 to 90 minutes, stirring every 30 minutes, until smooth.
If the queso is too thick, stir in hot water or milk 1 tablespoon at a time.
Switch to warm and stir every 20 to 30 minutes while serving with tortilla chips.