In a small bowl, whisk together the mayonnaise, ketchup, yellow mustard, sweet pickle relish, white vinegar, garlic powder, and onion powder to make the burger sauce. Set aside.
Thinly slice the onion and cook over low heat in butter or oil until deeply caramelized.
Warm the Keystone Beef in a skillet and season with the taco seasoning.
Spread kettle chips evenly onto a pan or oven-safe tray.
Spoon the hot ground beef over the chips, layer on the American cheese slices, and place briefly in the preheated oven until the cheese is melted.
Drizzle generously with the prepared burger sauce, top with caramelized onions, and serve immediately.