Most countries will have a "duty free" allowance that applies to most people entering the country. This allowance will cover good bought outside of the country, as well as goods bought at Duty Free stores on arrival into the country.
For the UAE specifically, the allowances are :
- 4 litres of alcohol or one carton / 24 cans of beer
- AED 2,000 worth of cigarettes or 400 sticks of cigarettes
- AED 3,000 worth of cigars
- 2 kilograms of tobacco
- AED 3,000 worth of gifts, including perfume
If you go over these limits, you will generally be required to pay duty and taxes.
Presuming the electronics you are buying are not gifts for someone within the UAE, none of those categories are relevant to you, so you will not need to pay duty on them.
That said, it is unlikely that you will find a good price for what you are intending to buy at Dubai Duty Free, especially on arrival (where, as per my answer to your other question, GST is still charged). You will most likely find a better price elsewhere within the city, or on a website like http://uae.Souq.com or http://www.carrefouruae.com