The way it was explained to him by the ariel fitter is as follows -
It 'switches on the ariel'
It plugs into your mains supply and has another lead which you plug into one of the 4 outlets in the new socket which leads to the multi ariel.
This is it-
Triax TMPR Power Supply Unit
PS -so I misled you - not a booster - a power supply for the ariel