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

Here is Why You Need An Adapter

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

Papua New Guinea

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

Type I

Thailand

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

Type A

Type B

Type C

Type O