You Do Need power plug adapter while traveling from Réunion to Bhutan.

Here is Why You Need An Adapter

The outlet and plug type used in Bhutan are C, D and G and in Réunion are C and E. This is how they look like.

Réunion

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

Type C

Type E

Bhutan

In Bhutan, outlets of type C, D and G are in use.

Type C

Type D

Type G