You Do Need power plug adapter while traveling from Thailand to Papua New Guinea.

Here is Why You Need An Adapter

The outlet and plug type used in Papua New Guinea is I and in Thailand are A, B, C and O. This is how they look like.

Thailand

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

Type A

Type B

Type C

Type O

Papua New Guinea

In Papua New Guinea, outlets of type I are in use.

Type I