ChinaTravelGuide is NOT accurate, I bought a high-speed train due to thier wrong information- please update!
Not every high-speed train in China has power outlets in each seat. I’m on an overnight D train from Shenzhen to Shanghai, there are only power outlets in the sleeper sections, in the 2nd class cabin there are two power outlets in the bathroom/sink area only.
From TravelChinaGuide
[…] and electrical sockets are available in each row or compartment.
Clicking further on the same site (link thanks to @pnuts in comments)
Battery Charging
Long journey can often be boring and passengers like to take along laptops or mobiles which depend on batteries. For your convenience you will find that these batteries can be re-charged from sockets in the aisle-side seats.
Complete with a photo. I also remember from personal experience some 3-4 years back finding and using these sockets.
What I find even better is that apparently also the slower long-distance trains are now equipped with sockets, something that was not quite the case last time when my train ran two days late.
Power is available on all air-conditioned trains (K, T, & Z) by the Spring Festival of 2014 (January 30th 2014). In soft sleeper and luxury soft sleeper coaches, passengers can recharge their phones with the power socket in their compartment or the two in the aisle. Hard sleeper coaches have two sockets at the end of the aisle. There is no socket in hard seat carriages, but one is available in the conductor’s cubicle. Passengers are able to recharge their mobile phones, laptops, tablet PCs, and electric razors. However, high-power electrical appliances, such as induction cookers and electric cookers, may not be used.
Credit:stackoverflow.com‘