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

Here is Why You Need An Adapter

The outlet and plug type used in Nepal are C, D and M 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

Nepal

In Nepal, outlets of type C, D and M are in use.

Type C

Type D

Type M