You Do Need power plug adapter while traveling from Japan to Uruguay.

Here is Why You Need An Adapter

The outlet and plug type used in Uruguay are C, F and L and in Japan are A and B. This is how they look like.

Japan

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

Type A

Type B

Uruguay

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

Type C

Type F

Type L