Gather the ingredients. Preheat an outdoor grill for medium heat and lightly oil the grate.

Place a 24-inch long piece of heavy-duty aluminum foil on a flat work surface. Spread potatoes onto the middle of the foil. Drizzle vinegar and olive oil over potatoes; season with onion powder, salt, and pepper. Distribute butter chunks evenly over potatoes.

Bring two shorter edges of the foil up and around potatoes; fold together several times at the top to create a seam. Fold the remaining two edges to seal the packet.

Place packet of potatoes (with the seam facing up) on the preheated grill. Cook until potatoes are tender, about 25 minutes, turning and shaking the packet several times during cooking to redistribute potatoes.

Remove from the grill and keep packet sealed until ready to serve. Be careful when opening as potatoes will be very hot and steam will release quickly.