1Heat oven to 350°F (325°F for dark or nonstick pan). Spray bottom only of 13x9-inch pan with baking spray with flour. Measure 1/2 cup of the cake mix into medium bowl; set aside.
2In large bowl, beat remaining cake mix, 1/3 cup butter, the vanilla and 1 egg with electric mixer on low speed until crumbly. Press dough in pan. Sprinkle with chocolate chips; press into dough.
3Add melted butter and 2 eggs to reserved cake mix. Beat on medium speed until smooth. Stir in pecans. Spread mixture over crust.
4Bake 24 to 28 minutes or until center is set. Cool completely, about 1 hour. Sprinkle powdered sugar over top. For bars, cut into 8 rows by 4 rows. Store covered.