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

Here is Why You Need An Adapter

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

Iran

In Iran, outlets of type C and F are in use.

Type C

Type F

Guam

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

Type A

Type B