Cut the processed cheese into 1-inch cubes.
Combine the cubed cheese, cheddar, undrained tomatoes with green chilies, milk, cumin and garlic powder in a medium saucepan.
Cook over medium-low heat, stirring often, for 8 to 10 minutes until completely melted and smooth. Do not boil.
Thin with milk a tablespoon at a time if needed, or simmer gently to thicken.
Taste, add salt if needed, and finish with a squeeze of lime if you like.
Pour into a warm bowl, add toppings, and serve immediately with tortilla chips.