You Do Need power plug adapter while traveling from Mauritania to Tuvalu.

Here is Why You Need An Adapter

The outlet and plug type used in Tuvalu is I and in Mauritania is C. This is how they look like.

Mauritania

In Mauritania, outlets of type C are in use.

Type C

Tuvalu

In Tuvalu, outlets of type I are in use.

Type I