To prepare the shrimp: Using the flat side of a knife, gently press down to slightly flatten each shrimp. Season with the salt and white pepper.
To prepare the rice paper: Using kitchen shears, cut each rice paper sheet into quarters. Keep the rice paper dry; there's no need to soak it.
To assemble the shrimp chips: Lay one piece of dry rice paper flat and place a flattened shrimp in the center with the tail sticking out. Cover with another piece of rice paper and gently press together. Repeat with the remaining shrimp and rice paper.
To make the sweet and sour dipping sauce: In a small pot over medium heat, combine the water, rice vinegar, ketchup, sugar, and salt. Bring to a simmer. Mix the cornstarch with 3 tablespoons water, then stir the slurry into the sauce and cook until thickened. Set aside.
To fry the shrimp chips: In a wok over high heat, heat the cooking oil to 375°F (191°C). Carefully add a few shrimp chips at a time and fry for about 1 minute, until the rice paper is puffed and crispy and the shrimp is pink and completely cooked through. Remove and drain. Repeat with the remaining shrimp chips.
To serve: Serve immediately with the sweet and sour dipping sauce.