Because you can't throw around "always" that easily, there are too many exceptions.
First of all, explain how things can be that equal between a turbo and a supercharger. Equal how? Boost level? A small turbo can make less power at a given boost level than a supercharger, if the turbo can't flow enough or heats the intake air too much.
So now you start having to make big assumptions so that your statement actually holds true.
What size is the turbo, what size is the supercharger, which is more efficient, how have you defined what the best turbo/SC for your intended power target is, what type of exhaust, what's the VE (vol eff) of the engine, what type of supercharger is it, what type of drive system does it have, what's it's drive ratio, is there an intercooler, is one setup intercooled but not the other, how efficient is the intercooler, etc.
How can you make all these things be equal?
How do you define more power? More peak power, more power over the whole RPM band, more power at a certain RPM?