Preheat the broiler. In a small bowl, combine the mayonnaise, chili powder and 1/4 teaspoon salt. Grease a 9-inch square baking dish with 1 teaspoon of the mayonnaise mixture. Place the tilapia fillets in the baking dish and coat with the remaining mayonnaise mixture. Top with the corn.
Broil until the corn is lightly browned and the fish is cooked through, about 10 minutes. Serve with the lime wedges.