Inertial supercharging effect is the result of incoming fuel/air charge developing momentum greater than intake stroke would generate alone. It is achieved by a combination of head/port configuration, and cam profile/valve timing.
The inertial supercharging effect from two-stroke engines is the result of the design of an expansion chamber in the two-stroke exhaust system. Its spiraled inside design was designed to turbulate the exhaust gas and create a vacuum that rips the exhaust gas out of the engine, bringing engine on to a "powerband" in high load situations. As every action has a reaction, by ripping the exhaust gasses out of the engine combined with the effects of the reeds, you are in turn ripping more fuel-air mixture into the combustion chamber, creating a supercharged power delivery effect IE "powerband". This is why the two-stroke engine is preferred by many motorcycling enthusiasts world wide.