Combine the pumpkin, onion, and bell pepper in a large bowl and mix thoroughly.

Whisk together the cornstarch, flour, salt, and black pepper in a separate medium-sized bowl until uniform.

Stir the dry flour mixture into the pumpkin mixture until the vegetables are well coated, then carefully pour in the water. Mix until the batter holds together—it should be thick, but if the pumpkin releases its own liquid and the mixture feels too wet, add another tablespoon or two of flour to help it bind.

Combine the vinegar, salt, sugar, black pepper, diced red onion, and sliced chile in a small bowl, stirring until the sugar has completely dissolved.

Heat enough oil in a large skillet over medium-high heat to submerge the fritters. The oil is ready when it shimmers and looks thin.

Scoop a portion of the vegetable mixture and flatten it in your palm until it is about a half-inch thick, then carefully slide it into the hot oil.

Fry the fritters for about 3 minutes per side until the edges are deep golden brown and crisp, using a spatula to keep them flattened while they cook.

Remove the fritters and transfer them to a strainer or wire rack to drain any excess oil—avoid covering them so they don't steam and become soggy. Serve immediately while hot and crackling with the vinegar sauce for dipping.