You Do Need power plug adapter while traveling from United States of America (US) USA to Spain.

Here is Why You Need An Adapter

The outlet and plug type used in Spain are C and F and in United States of America (US) USA are A and B. This is how they look like.

United States of America (US) USA

In United States of America (US) USA, outlets of type A and B are in use.

Type A

Type B

Spain

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

Type C

Type F