What do you mean by "chocolate powder"?
Like a pudding mix?
Like cocoa powder?
Use what the recipe calls for, and if you don't want to make a white cake, find a recipe for chocolate cake.
Or if you are working off of a boxed mix, go to the store and buy a chocolate cake mix.
(Boxed mixes make a cake that is very inferior, compared to homemade from-scratch cakes).
Cocoa has no sugar in it, and is very bitter if you don't adjust your sweetening.
If this is a cake mix, you cannot make it work out the way you want. Sweetening needs to be adjusted at the first step, where you "cream" together the butter and sugar with an electric mixer.