For additively weighted Voronoi Diagram: Remember that a power diagram in dimension n is only a(n unweighted) Voronoi diagram in dimension n+1.
For that, just recall that the Voronoi diagram of a point set is invariant if you add any constant to the coordinates, and that the weighted Voronoi diagram can thus be written as a non weighted Voronoi diagram using the coordinates, for example in 2D lifted to 3D:
(x_i, y_i, sqrt(C - w_i))
where w_i is the weight of the seed, and C is any arbitrarily large constant (in practice, one just small enough such that C-w_i is positive).
Once your diagram is computed, just discard the last component.
So, basically, you only need to find a library that is able to handle Voronoi diagrams in dimension n+1 compared to your problem. CGAL can do that. This also makes the implementation extremely easy.