The main problem with cakes in China, at least to me, is that they do not use wheat flour to make the cake, so from base ingredients already they taste different.  Also, in at least USA, chocolate is normally sweeten by adding milk, and this is why they look light brown instead of dark as European Chocolate.

Most cakes here are done at local bakeries.  You order them today and pick them up tomorrow.  Also, many are sort of part off or totally either ice cream inside or like a pudding.  My guess is that you will have to order a few small ones, on a trial basis, to see if you can find one bakery that will make something you like it.  My GF loves chocolate cake, and for New Year's Eve wanted one.  I order it from a local restaurant (they do make their own cakes), and to her it was exquisit, to me it was acceptable.  The chocolate shavings all over tasted like powder to me.  But I am very picky with chocolate tasting.

Cakes and French bread are two things Chinese bakeries have not master yet in my book.

I find the bakery at the Shuangjing station (Line 10 - exit A) really good

I havent got any real chocolate cake in any bakeries in shanghai..if u want really really choco thing-guess u have to visit a 4-5 star hotel ..with a little chance u can fall on one...true the cake base they make here is mainly sponge cake(eggs n flour),so it is indeed difficult to find the real cake we are so used to...well one advantage definitely is that the sponge cake is contains less fat than the normal cake .

For the cost of a good cake here you could make your own - and that includes the cost of the oven.