I'll be at Yubei Qu, Chongqing Shi, where are nearby good shopping malls for electronics & GPSs?

Well, as I know, there is no large such market in Yubei District.
So you can go to Chongbai Electronic Market. There are many stores that sell all kinds of electronic products with accpetable price. Generally speaking, the prices are lower than big shopping malls. The market is located at No.86, 3rd Zhongshan Road, Yuzhong District.

About clothes, Chaotianmen Clothes Wholesale Market is a good choice for you. You can find all kinds of fashionable and cheap clothes there. The address is No.16-22, Shidai Tianjiao Building, Chaoqian Road, Chaotianmen, Yuzhong District.