Powdered sugar is milled granulated sugar. It is also called confectioners’ sugar or 10x sugar, which means the sugar is fine and sifted ten times. The sweetness of powdered sugar depends on the amount of added starch. Starch is added to prevent the sugar from clumping. The more starch, the less sweet the sugar will be. It is best to buy a good-quality powdered sugar with little starch. In recipes, always start with a little less powdered sugar than called for, to account for the different levels of sweetness. Taste while working and add more if desired. In my experience, tried-and-true brands that have been around for generations, for example, Domino, yield excellent results.