You Do Need power plug adapter while traveling from Tonga 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 Tonga is I. This is how they look like.

Tonga

In Tonga, outlets of type I are in use.

Type I

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