Peel and cube sweet potatoes. Place in a steamer and steam for 10 minutes until soft. Transfer to a large bowl and mash with a potato masher.
Add glutinous rice flour, white rice flour, granulated sugar, and baking powder to the mashed sweet potatoes. Mix with a spatula until a soft dough forms. If dough is still a little wet, mix in some additional white rice flour. Dough should be soft but not sticky.
Pinch a little dough from the bowl and roll between palms to form a 1-inch diameter ball. Repeat until all dough is used up.
Fill a medium sized saucepan with 1 inch vegetable oil over medium low heat. Gently drop a few sweet potato balls into the hot oil. Fry for 3 to 4 minutes until golden brown. Sweet potato balls should float when cooked. Remove with tongs and drain on a metal strainer. Repeat until all sweet potato balls are cooked.