You Do Need power plug adapter while traveling from Turks and Caicos Islands to Saint Helena.

Here is Why You Need An Adapter

The outlet and plug type used in Saint Helena is G and in Turks and Caicos Islands are A and B. This is how they look like.

Turks and Caicos Islands

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

Type A

Type B

Saint Helena

In Saint Helena, outlets of type G are in use.

Type G