Mexico City - Electronics

You can find electronics and computers in all large stores like:

Walmart
Chedraui
Liverpool
Sears
Palacio de Hierro
Office Max
Office Depot
lumen (computers)

Mostly the prices are the same, but it might be worth a try to look around for special offers, which some of them always have.  On weekends some stores promote different items to attract more customers.

In case you decided to bring your electrical appliances with you but are faced with the different voltage, you can visit:

Radio Shack
Centro Comercial Santa Fe
Av. Vasco de Quiroga 3800
Col. Santa Fe, Mexcio
Tel: + 52 (55) 5259 7890
Fax: + 52 (55) 5250 8102
Or look for one RadioShack near you.
The usually carry different voltage converters.

Another place to look, would be Liverpool or Sears.