Put sugar and water in separate bowls. Separate spring roll wrappers; stack. Peel plantains; cut in half and then half again lengthwise.
Place 1 wrapper on a clean work surface with 1 corner facing you. Coat 1 plantain piece in sugar; place 1 inch from the near corner of the wrapper. Fold corner over the plantain; roll up halfway. Fold in 2 side corners; continue rolling until near the top. Moisten top corner with wet fingers; finish rolling. Repeat with remaining wrappers.
Heat oil in a deep-fryer or large saucepan to 350 degrees F (175 degrees C). Place egg rolls in a single layer; fry until golden brown on the bottom, 2 to 3 minutes. Flip; sprinkle with brown sugar. Fry 2 to 3 minutes more. Transfer egg rolls to a plate.
