You Do Need power plug adapter while traveling from Pitcairn Islands to Congo.

Here is Why You Need An Adapter

The outlet and plug type used in Congo are C, D and E and in Pitcairn Islands is I. This is how they look like.

Pitcairn Islands

In Pitcairn Islands, outlets of type I are in use.

Type I

Congo

In Congo, outlets of type C, D and E are in use.

Type C

Type D

Type E