I would assume there is a 110v-240v feed available already otherwise what would the lighting and other systems come off.
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Low voltage supplies for public use are a totally different proposition to those powering essential on-board services. All items of equipment that form part of a train's electrical systems are:
a) of known electrical load range,
b) power factor,
c) surge immunity,
d) maintenance status
e) and reliability
Accordingly, supplies are provisioned on that basis. That was the issue (mainly affecting safety) regarding the 'Not for Public Use' three-pin outlets that the arrogant twit on the LO train was cautioned for unauthorised use last year. Lighting, door controls, heating and AC may be used by the public, but they have no means of connecting directly to their power supplies.
Without know the exactly facts I would still hasten to point out that in my opinion any track wear as a result of a few plug sockets would be very minimal and would not cause an issue to the public purse especially as the weight differential with and without plug sockets in the grand scheme of things when a 12 car is fully laden with passengers will be very small.
You may be right over the effect of additional track wear, however the convoluted methods whereby the pseudo-privatisation's costs are allocated and priced may mean that it has a disproportional effect on the TOC, the infrastructure maintainer or the DfT's budgets.
The potential costs of providing at-seat power for passengers goes way beyond overall train weights though. Providing some power to many locations without any real control over what loads are connected has many complications:
1) every outlet must fully conform to electrical standards for domestic supplies which may not be the case for all low voltage services on a train. This dictates the use of dedicated inverters connected to non safety-critical or operationally important busbars
2) every outlet must fully conform to mandated EMC standards both in immunity and emissions to protect both passenger's connected devices and on-board systems
3) a diversity must be applied to all possible loads on every outlet, as the operator has no control over what will be connected to them. This is the most difficult aspect to reconcile as for example, the maximum reasonable load would be a notebook pc. Now although laptops typically use between 60W and 100W DC from their ac power packs, those power packs have a corresponding ac current draw between 1.2A and 1.6A at switch-on.
So if the current is set to a nominal 2A per outlet, each circuit, (radial or ring) would be limited to no more than 15 outlets so each coach would require three or four separate circuits.
Now rail passengers are not known for their compliance with rules, and of them, some commuters are not known for their consideration of others (particularly when they think that their actions are anonymous), so each outlet would need some form of current trip to prevent a greater load being placed on some outlets. Therfore each outlet socket couldn't be a £10 standard item from Screwfix or any other domestic device supplier. They would require an auto resetting current trip on each, (preferably with a bleeper to let all the other passengers know what the selfish twit had tried to do!
).
All of this kit would require both electrical and mechanical qualification (type approval), and individual testing of each unit before delivery, as well as being integrated into the regular maintenance regime.
In summary, it won't be a case of a few cheap bits from Screwfix and a bit of wire connected up to the train's normal default voltage supplies because it 'will only be providing bug-power to a few mobile phones'. It would be cheaper for the TOCs to issue free portable charger/batteries to every season ticket holder, leaving them with the simple task of remembering to charge them at the office or at home.
