While the average consumer in the US will shop at a chain like Best Buy for their electronics or order online, in Shanghai it's generally much more convenient to go to an electronics market. They usually consist of several floors and hundreds of stalls, selling everything imaginable: mobile phones, cameras, laptop and desktop computers, computer parts and peripherals, televisions, MP3 players, GPS systems, e-readers, games consoles and games, etc.
Most stalls will often offer repair and other services (e.g. phone unlocking/jailbreaking), so if you want to buy a device or have a problem with one, electronics markets are usually the place to go.
While there are plenty of small electronics markets throughout the city, the three largest and diverse electronics markets are the Pacific Digital Plaza and Metrocity at Xujiahui, and the Da'Ao Communications Mall near Shanghai Railway Station.
Pacific Digital Plaza
太平洋数码广场 (tàipíngyáng shùmǎ guǎngchǎng)
1117 Zhàojiābāng Lù, Xuhui / 徐汇区肇嘉浜路1117号
Map | Xujiahui
This huge electronics market houses everything you might need. As one of the oldest electronics markets in Shanghai, it has undergone many renovations over the years and as such is fairly well maintained compared with many smaller markets. There are actually two Pacific Digital Plazas - I and II. PDP I focuses primarily on PCs and components, whereas PDP II has a wider variety of electronic devices like cameras and mobile phones. The two markets are pretty much within spitting distance of each other.
The easiest way to get here is to take the metro to Xujiahui station and head towards exit 10, which goes straight into the basement floor of PDP II.
The massive glass globe on the building's facade makes Metro City pretty hard to miss. Metro City is actually a shopping mall that happens to have a sizeable electronics market - there is a large food court on the bottom floor, a cinema, and many other stores inside.
The electronics market inside Metro City is pretty similar to that of PDP - different sections house different categories of devices. Generally speaking, Metro City has a better selection of video game consoles and games, as well as high-end cameras. However, your mileage may vary. Between Metro City and PDP you pretty much have all your bases covered.
Da'ao Communications Mall
大奥通讯商城 (dà'ào tōngxùn shāngchéng)
547 Tiānmù Xī Lù, Zhabei / 天目西路547号
Map | Shanghai Railway Station
Covering over 20,000 square metres and with more than 1,000 stalls, the Da'ao mall has plenty of electronics but specialises in mobile phones. Generally speaking, it's the best place in the city to buy a new handset or get a phone repaired.
Several /r/shanghai users have recommended Steven Chen in the Da'ao Mall as a trustworthy person to see about buying/repairing a phone, with the added advantage that he speaks good English and is contactable on WeChat, with the username chenyuerui1983. This has the added advantage of being able to ask beforehand if he can help you out, or knows anybody who can.
陈慧君 (Chén Huìjūn) at stall 175 has also been recommended as a good option for phone repair.
Xing Guang Photography Equipment Center
星光摄影器材城 (xīngguāng shèyǐng qìcái chéng)
288 Lǔbān Lù, Luwan / 鲁班路288号
Map | Luban Lu
On the corner of Lǔbān Lù and Xiétǔ Lù is a huge mall with 6 floors of photography equipment. The first two floors are filled with shops and stalls selling new cameras from all the well-known brands, whereas the other floors cater to second hand cameras, accessories, repair services, and specialist equipment.
- As is usual with markets in China, don't forget to haggle to get the best price. Sellers will be keener to offer you a better 'bundle' price if you buy several items from them; so if you're buying a phone it's usually a good idea to look at cases, memory cards, spare cables/chargers, etc. at the same time.
- Try every item before buying and check it thoroughly to ensure it isn't a fake. Reputable sellers will have no problem with you trying something before you buy it.
- Make sure you ask for a 发票 (fāpiào - "receipt"), which will usually be a hand-written proof of purchase. It's also a good idea to get a 名片 (míngpiàn - "business card") from anybody you buy something from so you can find them again easily if anything goes wrong, or easily recommend them to somebody if they provided good service. Business cards will almost always have the seller's name, phone number, and stall number.