You Do Need power plug adapter while traveling from Tonga to Cambodia.

Here is Why You Need An Adapter

The outlet and plug type used in Cambodia are A, C and G and in Tonga is I. This is how they look like.

Tonga

In Tonga, outlets of type I are in use.

Type I

Cambodia

In Cambodia, outlets of type A, C and G are in use.

Type A

Type C

Type G