Rinse julienned potatoes two or three times, until the water runs clear. Cover with water, and set aside. Stored in refrigerator, potatoes can be prepared up to two days ahead.
Drain potatoes and pat dry with towels.
Heat oil in a large skillet over high heat until rippling. Add whole dried chiles and scallion and sauté until fragrant, about 60 seconds. Add Sichuan peppercorn, if using, and stir again.
Add potatoes, stir, and cook for 2-3 minutes, until shreds go from stiff to floppy. Add fresh chile or bell pepper and sauté another 90–120 seconds, until fresh chiles start to soften.
Add vinegar, soy sauce, salt and sugar and stir-fry to tender-crispness, 60-120 seconds. Remove from heat, plate, and serve warm.
