Preheat the oven to 350 degrees F. Butter a 9x13-inch baking or casserole dish.
In a large bowl whisk together the cream cheese, mayonnaise, Parmesan, garlic powder and chili powder.
Add the corn, Ro-tel and both cheeses - holding back a handful to scatter over top.
Stir well and spread out evenly in the pan. Sprinkle the handful of cheese over the top.
Bake 28 - 35 minutes until bubbly around the edges. The grease from the cheese will rise to the top - skim it off with a spoon and discard.
Garnish with green onions.
Serve warm with tortilla chips.