You Do Need power plug adapter while traveling from Switzerland to Guam.

Here is Why You Need An Adapter

The outlet and plug type used in Guam are A and B and in Switzerland are C and J. This is how they look like.

Switzerland

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

Type C

Type J

Guam

In Guam, outlets of type A and B are in use.

Type A

Type B