As of 2015, you can value vintage porcelain table lamps by getting a free appraisal through Barnebys, which is an auction search service with connections to more than 400 affiliated auction houses. Sign up for a free account, snap a photo of the lamp, fill in other relevant information, and then send it to Barnebys so they can pass it onto their affiliated auction houses. You will receive an answer from one of their experts.
Alternatively, you can try to value vintage porcelain table lamps on your own by comparing them to similar lamps that sold in the past. Start by checking the lamp for either a sticker, a stamp or some other mark that can be used to figure out its maker, which can usually be found on its bottom. Once you know who made the lamp, start checking it for signs of damage as well as signs of repair that can negatively affect its value. Use caution when checking electrical parts. For example, if the power cord is frayed, do not plug the lamp into a socket to see if it still works.
With this information, you can find similar lamps that sold in the past. Once again, Barnebys can be useful with its extensive database of sale prices, and there are other collectors sites that provide similar services.