Melt butter in a saucepan over medium heat. Whisk in flour and cook for 1-2 minutes, stirring constantly.

Slowly whisk in the evaporated milk. Continue to whisk until the mixture begins to thicken.

Add cream cheese and stir until melted and smooth.

Add cheddar cheese a handful at a time, stirring until fully melted and combined.

Mix in the diced tomatoes with green chiles, garlic powder, onion powder, and cayenne pepper.

Heat through, then transfer to a bowl or slow cooker and serve warm.