Preheat the oven to 350 degrees F. Coat a 9-inch square baking pan with cooking spray.
Beat together the confectioners' sugar, peanut butter, cream cheese, 1/2 teaspoon vanilla extract and 1 egg in a large bowl with an electric mixer on medium-high speed until smooth.
In a small bowl, combine the flour, cocoa powder, baking powder and salt. Whisk to thoroughly combine.
In a medium bowl, whisk together the remaining 2 eggs, granulated sugar and remaining 1 teaspoon vanilla. Whisk in the butter.
Add the flour mixture and chocolate chips to the bowl with the egg-butter mixture and fold together with a spoon or spatula until just combined.
Add half of the brownie batter to the pan and tap on the countertop to level. Add the peanut butter mixture by the spoonful, making sure that the spoonfuls do not touch each another. Pour the remaining brownie batter over the top and swirl the two batters together with a butter knife.
Bake until the edges are just set, about 20 minutes. The center should still be soft. Cool in the pan for at least 15 minutes before cutting.