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

Here is Why You Need An Adapter

The outlet and plug type used in Yemen are A, D and 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

Yemen

In Yemen, outlets of type A, D and G are in use.

Type A

Type D

Type G