In a large bowl, whisk together the flour, cornmeal, baking powder, sugar, salt, onion powder, and garlic powder. In a large glass measuring cup, stir together the grated onion, buttermilk, and egg. Add the liquid ingredients to the dry and slowly stir together until the dry ingredients are just combined. Set aside until mixture is puffed and light, about 60 minutes.
2. Pour enough vegetable oil that it reaches 2" up the sides of an 8-qt. saucepan and heat to 350° on a deep-fry thermometer. Using a tablespoon, drop small rounds of batter into the oil, making sure to not crowd the pan. Cook, stirring occasionally and flipping halfway through, until golden on the outside and crisp, about 2 minutes. Remove hush puppies from the oil and drain on a cooling rack set over a paper –lined baking sheet. Repeat with remaining batter.