Using a food processor fitted with a coarse grating disk, grate the potato and onion; discard any large pieces. Transfer the mixture to a clean dish towel and squeeze out any excess liquid, then transfer to a large bowl. Stir in the flour, egg, 3/4 tsp. salt, 1/4 tsp. pepper and the baking powder.
In small bowl, combine 2/3 cup finely chopped fresh pineapple, 2 tbsp. finely chopped jalapeno, 1 tbsp. finely chopped red onion, 1 tsp. fresh lime juice, 1/2 tsp. lime zest and pinch salt. Stir in 3/4 cup shredded unsweetened coconut to grated sweet potato-onion mixture.
In a medium skillet, heat 1/4 inch oil over medium-high heat until hot but not smoking. Working in 5 to 6 batches, drop 2 tbsp. scoops of batter into the pan about 2 inches apart. Using a spatula, flatten the batter into disks. Cook, turning once, until browned and crisp, about 5 minutes. (Lower the heat if the latkes darken too quickly.) Drain on paper towels. Serve with pineapple relish.