Boil diced potato in salted water for 10 minutes until very tender. Drain well and let steam dry for 1 minute.
Mash potato until completely smooth, then spread on a plate to cool for 5 minutes.
In a large bowl, combine crab meat, cooled potato, cilantro, green onions, chili, garlic, fish sauce, lime juice, lime zest, egg, white pepper, and salt. Mix gently until combined.
Form mixture into 8 patties (about ¼ cup each), roughly 2½ inches wide and ¾ inch thick. Refrigerate 15 minutes if mixture feels too soft.
Heat oil in a large nonstick skillet over medium heat. Add patties without crowding the pan.
Cook 3-4 minutes per side until deep golden brown and crispy. Don't flip too early.
Drain briefly on paper towels, then serve hot with sweet chili sauce, lime wedges, and fresh cilantro.