You Do Need power plug adapter while traveling from Saint Helena to Chad.

Here is Why You Need An Adapter

The outlet and plug type used in Chad are C, D, E and F and in Saint Helena is G. This is how they look like.

Saint Helena

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

Type G

Chad

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

Type C

Type D

Type E

Type F