Whisk the mayonnaise, chili-garlic sauce, and vinegar together in a small bowl until smooth. Add more chili-garlic sauce if you prefer a sharper kick, then set aside for the flavors to meld.

Bring 2 quarts of water to a boil in a large pot. Add the salt, baking soda, and sweet potatoes. Simmer until the potato exteriors are just tender but the centers offer resistance when pierced with a paring knife, about 5 minutes.

Drain the potatoes thoroughly and spread them in a single layer on a rimmed baking sheet. Let them air-dry while you prepare the coating; this prevents the slurry from becoming too thin.

Whisk the cornstarch and 1/2 cup of water in a large bowl until a smooth, milky slurry forms. Add the parboiled potatoes and toss gently by hand until every wedge is evenly coated.

Heat the oil in a large nonstick skillet over medium-high heat until it reaches 350°F—a potato wedge should sizzle vigorously the moment it hits the oil. Carefully add half of the potatoes to the skillet. Fry, turning occasionally with a slotted spoon, until the fries are deep golden brown and the coating feels rigid and crisp, about 8 to 10 minutes.

Transfer the finished fries to a wire rack set over a baking sheet to drain. Season with extra salt immediately while the surface is still hot so it sticks. Return the oil to 350°F and repeat with the remaining potatoes. Serve hot while the crust is still crackling, with the dipping sauce on the side.