You Do Need power plug adapter while traveling from São Tomé and Príncipe to Marshall Islands.

Here is Why You Need An Adapter

The outlet and plug type used in Marshall Islands are A and B and in São Tomé and Príncipe are C and F. This is how they look like.

São Tomé and Príncipe

In São Tomé and Príncipe, outlets of type C and F are in use.

Type C

Type F

Marshall Islands

In Marshall Islands, outlets of type A and B are in use.

Type A

Type B