If you have the same item / power equipped and in the Cube, the value on the equipped item is used, i.e. even if the Cube value was 65%, if the equipped one is 50%, you get 50%.
If you have the same item / power equipped and in the Cube, the value on the equipped item is used, i.e. even if the Cube value was 65%, if the equipped one is 50%, you get 50%.