(from http://www.onlineconversion.com/forum/forum_1060894343.htm)
sugar, brown 200 grams/cup
sugar, castor 190 grams/cup
sugar, confectioner's 130 grams/cup
sugar, granulated 190 grams/cup
sugar, powdered 130 grams/cup
Hence, if the internet is right (???), there is no difference...