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

Here is Why You Need An Adapter

The outlet and plug type used in Sint Eustatius are A, B, C and F and in Guam are A and B. This is how they look like.

Guam

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

Type A

Type B

Sint Eustatius

In Sint Eustatius, outlets of type A, B, C and F are in use.

Type A

Type B

Type C

Type F