As a railway engineer, I can perhaps help with the answer.
Trains such as the original High Speed train, and the Mk3 and Mk 4 (used on East Coast Main Line only) rolling stock provide a 415 AC supply which is intended for what are known as "hotel services" - air con, doors, lighting, restaurant vehicles, PA, etc. In the case of diesel powered trains (HST and locomotive hauled Mk3) the supply is derived from the traction unit main generator, and in the case of electric rolling stock (mainly ECML Mk4 now) the 415 volt supply is drawn from a tap from the main transformer at 25kV.
The power supply is then reduced down to 230 volts as required. For obvious reasons to supply is known as a "dirty" supply because it is not controlled and can be variable The sockets that you see principally in the luggage area intended ONLY for use when the train is switched onto a stabilised shore supply or when the train is stabled during a turn-round period and we can be certain that the power supply should be relatively stable. The sockets are there for cleaning equipment and any powered maintenance equipment.
These sockets are NOT under any circumstances to be used for passengers personal items such as mobile phones, laptops, etc, etc because the supply could suddenly surge and fry the item plugged in.
Newer trains have protected dedicated supply circuits that are safe for passengers to use and these can be found at seat points and table ends/table bays.
Hope this helps ?