Combine vinegar, brown sugar, ketchup, chile flakes, and ½ cup water in a small saucepan and bring to a simmer over medium-high heat, whisking to combine until sugar is dissolved.

Combine remaining tablespoon water and cornstarch in a small bowl and whisk with a fork to form a slurry. Whisk into sauce and bring to a boil. Allow to cool.

Combine cream cheese, crab, and scallions in a medium bowl and fold with a spatula.

Lay one wonton wrapper out on a cutting board (keep the rest under plastic wrap or a damp towel) and place a small amount of filling in the center (about 1 ½ teaspoons). Moisten the edges and seal.

Transfer to a large plate, cover loosely with plastic wrap, and repeat until all of the filling is used.

To finish the sauce, add pineapple chunks and puree with an immersion blender or standing blender.

Heat oil in a wok or Dutch oven to 375°F (190°C). Carefully add 10 to 12 wontons to the oil and cook until crisp and golden brown, about 3 minutes.

Transfer to a paper towel-lined bowl to drain, season with salt, and serve immediately with sweet and sour sauce.