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

Here is Why You Need An Adapter

The outlet and plug type used in Poland are C and E 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

Poland

In Poland, outlets of type C and E are in use.

Type C

Type E