It should rise proportionally to the weight (mass airflow) of the intake air as it passes the intake valve. This is one area where some usage of the metric system is handy Say the engine makes 240hp at 4000rpm. Assuming we are at or near Mean Sea Level (MSL)and the atmospheric pressure is 14.7 psi or one atmosphere. If you add 14.7psi of boost, the engine horsepower output should double to around 480.

In reality it won't because it takes more power to run the blower and there are increases in friction and cooling system load, among other things. This is a really rough rule of thumb and could be viewed as the maximum power increase possible. Still, one should not equate a pound of boost with a single value of horsepower increase, which is what I am seeing here in some replies.
Put another way, one psi of boost increases power differently for different engines.

There's a whole lot more that I didn't cover, and a whole lot more that I just plain don't know. What I wrote in this post should be correct, as far as it goes.

The latest is the electric turbocharger. I could envision keeping the boost alive with a motor and then at some point the exhaust driven turbine takes over. The problem is it doesn't seem that there would be exhaust driving the impeller at any time.

R.