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

Here is Why You Need An Adapter

The outlet and plug type used in Laos are A, B, C, E and F and in Vietnam are A, B and C. This is how they look like.

Vietnam

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

Type A

Type B

Type C

Laos

In Laos, outlets of type A, B, C, E and F are in use.

Type A

Type B

Type C

Type E

Type F