You Do Need power plug adapter while traveling from Yemen to Greece.

Here is Why You Need An Adapter

The outlet and plug type used in Greece are C and F and in Yemen are A, D and G. This is how they look like.

Yemen

In Yemen, outlets of type A, D and G are in use.

Type A

Type D

Type G

Greece

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

Type C

Type F