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

Here is Why You Need An Adapter

The outlet and plug type used in Saint Helena is G and in Liechtenstein are C and J. This is how they look like.

Liechtenstein

In Liechtenstein, outlets of type C and J are in use.

Type C

Type J

Saint Helena

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

Type G