I fitted a dual USB and dual 12V adapter to the car inside the small storage space on the right of the steering wheel (RHD car). Just a small hole was necessary on the left inside the storage space. I attached the adapter to the top of storage space using extra strong adhesive velcro rated at 15KGs from Halfords. The idea being that I could easily remove the adapter when I eventually sell the vehicle and apart from the small hole drilled where it can't be seen, there would be no trace.
I wanted power that side of the steering wheel as I prefer my satnav and phone to my right and previously I had to drape wires in front of the steering wheel and down into the centre console binnacle (in this EGS vehicle).