You Do Need power plug adapter while traveling from São Tomé and Príncipe to Cuba.

Here is Why You Need An Adapter

The outlet and plug type used in Cuba are A, B, C and L and in São Tomé and Príncipe are C and F. This is how they look like.

São Tomé and Príncipe

In São Tomé and Príncipe, outlets of type C and F are in use.

Type C

Type F

Cuba

In Cuba, outlets of type A, B, C and L are in use.

Type A

Type B

Type C

Type L