From Shenzhen to Guangzhou is short trawel with fast train. (and not expensive)
Guangzhou have lot of. It is "electronics center". What ever you need you find it Guangzhou (or Guangzhou - Shenzhen area).
(If you want buy new electrnics equipments (outside china manufactured) maybe HK prices are more cheap... but other way HK is super expensive place if compare mainland China.)
Ask example some chinese ebay seller who location is Guangzhou (or also Shenzhen). Most of chinese peoples are very kind and maybe they help you if you tell you are visiting and need help for finding electronics (small business "super markets")
Western tourist itself is nearly impossible to find these places in China. (or you find just these places where you only lost you money.)
Take some chinese people to help you. With small money some kind chinese can call his friend and he call his frend and after half hour you know where they all are. Then take Taxi (DO NOT take fake taxi - this is first who you find) or citizen guide. With small money some guide can pick up you every place and he know friend who know etc.. (if you take guide look that he/she is honest) Do not try your self, you loose two days and you do not find anything. (they are not small 2 million peoples villages
)
In Guangzhou I find this system example one old mediumbig building. Inside building was maybe several hudreds of small electronic shops. Outside this building you can not quess what is inside. If you find this kind of place you need one week to look what all it have.
I can not tell address becouse I really do not know. It was not in "new centrum". Some "motorcycle "taxi" pick up me and my chinese wife to this place and after around thousand corners left and right.... Other problem is that if I tell one or two year old info... maybe there is not this street and building anymore and now over it is some modern 50 floor building.