Preheat the air fryer to 390°F for 5 minutes.
Stir together paprika, chili powder, garlic powder, onion powder, cumin, cayenne, sugar, salt, and black pepper.
Toss frozen fries with oil in a bowl. Sprinkle on about half of the seasoning blend and coat evenly.
Air fry fries in a single layer for 12–16 minutes, shaking the basket halfway, until golden and crisp. Cook in batches if needed.
Warm evaporated milk and butter in a small saucepan over medium-low heat until steaming, not boiling.
Whisk in cornstarch until smooth. Reduce heat to low and gradually stir in cheddar and American cheese until melted and velvety.
Stir in jalapeño brine. Taste and adjust salt or heat to preference; keep sauce warm on low.
Toss hot fries with remaining seasoning. Serve immediately with warm cheese sauce for dipping or drizzling.