I have been in Shanghai for almost 4 years and have always bought my electricals/electronics from Gome. They have different stores all over China but I always shop from the one at Zhongshan Park.,
They have genuine products/brands with variety to suit your budget, yet the price is much lower than their competitors Sunning or Yolo. Most of the products come with Protected content warranty but I have never been able to use my warranty certificates as everything from the ones I bought almost 4 years ago is in perfect working condition.
I highly recommend this store. They don't have many English speaking staff though. So, it would be helpful to go with a friend who speaks Chinese or carry your cellphone/electronic dictionary to translate. They have time to read your messages.