In a large bowl, combine the cake mix, flour, water, and eggs. Beat with an electric mixer on low speed for 5 minutes, or until batter is free of lumps.
Heat oil in a large, deep skillet until it reaches 375 degrees F (190 degrees C). Using a small scoop equal to about 2 tablespoons, carefully drop batter into hot oil in batches so as not to overcrowd.
Cook donuts in hot oil for 5 minutes, or until golden brown, flipping once with a fork mid-way through for even cooking.
Carefully remove donuts from oil with slotted spoon or tongs, and drain on paper towels. Dust with confectioners' sugar before serving.
