The largest outlet of Shanghai is located in Qingpu where so many top brands have set outlets. From downtown Shanghai, you could take the metro and get off at Sheshan stop of Line 9. Then, please hire a cab driving there, the fare of which is about CNY30.
Here are pictures of this Outlet: http://www.dianping.com/shop/1891930/photos

There is one factory outlet mall called "Fox Town". The name in Shanghai is called, "非洲广场". It's in the XuJiaHui district. You can take Line 1 or Line 4 to Shanghai Indoor Stadium and find one of the exits that go right under the mall itself.
I find that the prices there are pretty reasonable. :)