All of these sockets (in the dash cup holder, kitchen end panel, beside rear seat and lastly in the boot) are all 12 volt and accept a standard cylindrical plug. These are available from any car accessory shop or off the internet. The most common use is to use them with a USB adaptor to power/charge phones, laptops and also free standing Sat Navs. Very useful.
However, not to be confused with the 2 pin socket at the base of the B pillar behind the passenger seat. This is the continental design and powered by an inverter off the leisure batteries and produces 230 volts AC. This is a low power supply, so will only be able to supply up to 150 Watts, so a laptop is about it. As the inverter switched on when you plug something in, don't leave a cable plugged in if you are not using it. This will drain the batteries quickly, to no benefit to you.
The 13 Amp socket beside the 12 volt one on the end of the kitchen unit is only live when you are on hook up. Much more power is available subject to the limitations of the campsite 230vAC supply.
Hope this helps.
Alan