Combine potatoes, 1 cup vinegar, and 1 Tbsp. kosher salt in a medium saucepan; add water to cover by 1”. Bring to a boil, reduce heat, and simmer until potatoes are tender, 20–25 minutes; drain and pat dry.
Heat butter in a large skillet over medium-high heat. Add potatoes; season with kosher salt and pepper. Cook, tossing occasionally, until golden brown and crisp, 8–10 minutes. Drizzle with remaining 2 Tbsp. vinegar. Serve topped with chives and sea salt.