Travellers returning from the Canary Islands are treated at the customs like travellers from outside the European Union. Villalba Herv s, El Castillo, doctor Allart, Bethencourt Alfonso and San Jos as well as in the surrounding of Plaza de Espa a and Plaza de la Candelaria. They usually have a morning and afternoon timetable. There is a vast variety of cheap electronics on offer. I'm not sure about the quality but the brands are partly the same as in others countries.
Mobile phones are astonishingly inexpensive.
Whether they function in other countries or not I have no way of knowing. CD-players, car stereos and cameras are worth a closer inspection. The variety of watches is endless. Even the handsome Camel watches are real bargains. It is safer to buy the perfumes at your home airport when leaving for Tenerife or in the plane.