Hi Sheila
You can indeed buy Chinese Yuan in advance. Many main branches of Thomas Cook and Marks & Spencers Foreign Exchange have currency available over the counter, and most banks and post offices are able to order Yuan for you. You may also purchase Yuan at all major airports but the rate of exchange may not be as favourable.
You can take up to 6,000 Yuan to China, which is about £400. There is no limit on the amount of other currency you can take into China, but if the amount is over £2000, this must be declared to customs!
Regarding your question about the adapter, we recommend that you take a universal/ international adapter with you, as sockets vary quite a bit around China, and you'll also be able to use it wherever you go in the world in future. Ask the staff in the shop if you aren't sure which ones are which.
Kind regards,
Olly, your editor