Xi, Hu Jintao, Jiang Zemin, Li Peng, all had merely Bachelors of Engineering. Most of the current politburo have PhDs in normal political areas like Law, International Relations, economics, Political science.

after checking the current Politburo, I found the following people with PhDs in Engineering:

Chen Jining: Civil engineering

Yuan Jiajun: Aerospace engineering

in addition, the following have related graduate degrees:

Li Ganjie: Masters in Nuclear Engineering (?)

Li Qiang: Masters in Engineering Management

Liu Guozhong: “Graduate degree in artillery system fuse design and manufacturing”

Ma Xingrui: PhD in Mechanics