Cambridge, considering its prominence in the blue chip sector, is not overly graced with electrical shops. You will find most electrical stores based in and around the Retail Park on Newmarket Road. Here you will find Currys, PC World, with Dixons directly across Newmarket Road as well as Maplin Electronics at the Beehive Centre, a walking distance from the Retail Park.
I find Maplin to be cheaper for certain products as well as stocking a wide range of products. Currys and Dixons do however stock larger electrical products such as Hoovers or Televisions which Maplin don't. As a general rule of thumb you are better off visiting Dixons and Currys for larger electrical products, and Maplin for components with PC World being the best place to look for anything computer related, especially software.
Overall Cambridge isn't really the best place to go for electrical products as Currys/Dixons/PC World (all owned by the same group, along with The Link) hold the monopoly here so you are unlikely to be able to shop around and find a cheaper deal.
The City Center itself has a number of different mobile phone shops including The Link, Carphone Warehouse, Vodafone, 3, and O2. You are therefore much more likely to be able to shop around in this sector of the electrical market.