Following is an essay discussing the brief history of how has the Chinese(Mandarin) phonetic system metamorphosed from Wade-Giles into the standard Hanyupinyin, and the complications thereof:  "文摘：北京为什么是Peking 外国人怎么拼中国地名？" at http://www.guancha.cn/WenZhai/2016_01_14_348065.shtml

I really don't know much about any kinds of phonetic alphabet. (Otherwise, I would have got full marks of English test in high school entrance examination.)  All I know is the romanization phonetic symbols for spelling Chinese, the Wade-Giles system, had been primarily invented for foreigners to learn the brand-new but time-honored language to them.  Except Mandarin; however, China has had so many a dialect that the system had to adjust itself as to accommodate such a diversification.  I think that's why the system is unable to build up a standardized pronunciation for Mandarin, or ordinary spoken Chinese(普通話).  Does "Chang" really sound like "張" in Mandarin?  (Not to mention "Ng" for "吳" among some southern Chineses)

Then up came Zhuyin alphabets in 20's.  That had been a great helper in pronouncing and learning Chinese characters, especially in Taiwan after 1949.  But the system was so invented as a learning tool for Chinese people only.  Therefore, Wade-Giles still played an important role as the intermediary between Chinese and other foreign languages, particularly English, until that multi-functional Hanyupinyin emerged.  (Please also see my preivious writing "Happy Birthday, Mr. Zhou Youguang at http://blog.udn.com/kkuo0810/43350119. ) 

P.S.  Taiwan's Ministry of Foreign Affairs is still using Wade-Giles to transcribe the English names for passport applicants.  Now DPP will be back in office after May 20th; I hope they won't discard the Hanyupinyin names of those streets, roads, subway stations and secondary townships that has already had since Ma administration.  Please note Hanyupinyin is the ultimate solution for sure, just like final unification is an inexorable trend!