You Do Need power plug adapter while traveling from Pitcairn Islands to Vietnam.

Here is Why You Need An Adapter

The outlet and plug type used in Vietnam are A, B and C and in Pitcairn Islands is I. This is how they look like.

In Pitcairn Islands, outlets of type I are in use.

Type I

In Vietnam, outlets of type A, B and C are in use.

Type A

Type B

Type C

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