What is a 48-volt supercharger? Why do cars with turbochargers still need such a supercharger? A 48-volt supercharger is an electrically powered compressor which pressurises intake air to provide additional boost.
Being electrically powered, the supercharger responds immediately, requiring just half a second to spin to maximum speed (as in the case of the new Range Rover engine).
As a result, the engine receives boosted intake air at low speeds (just past idling). At these speeds, a turbocharger is merely gaining momentum and far from maximum output. So the supercharger's boost effectively fills a gap.
But the 48-volt power source is sustainable only for a short period. After which, the exhaust gas-driven turbo - having reached optimal speed - takes over.
Electrically powered superchargers are fairly new, having been made possible by lithium-ion batteries and 48-volt alternators.
Before them, there were engine-powered superchargers which, in principle, did the same thing.
But because they are attached to the engine (often by a belt), they exert an extra load on the engine. Hence, they are not as efficient as electrically powered compressors.