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

Here is Why You Need An Adapter

The outlet and plug type used in Guam are A and B and in Saint Martin are C and E. This is how they look like.

Saint Martin

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

Type C

Type E

Guam

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

Type A

Type B