The obvious choices to get your electronics are:
While they do sell the big brands as you noticed, you should be able to also find no-name products for quite cheap. For instance I've been able to find generic iMac chargers at Sim Lim for a good price.
Those malls are organised in a lot of small shops, so it is very easy to walk around and compare prices. However, note that it's also quite easy to get ripped off.
In my experience you can also get cheap electronics at other places. If you have enough time I'd definitely have a look at Mustafa Centre, a 24-hour mall which has almost everything.
Another option are small neighborhood shops, which are located at the heartland of the many HDB (public housing) estate. Those are however often off the beaten track and not so easy to find as a tourist. If your traveling from Changi Airport the city, you might for instance stop at Bedok MRT station, where one such heartland is located and try to find some electronics stores. (not the mall, but you have to cross the food-centre towards the stores that are located on the street)
However you'd have to be very lucky to find a store that is cheap and good. For that reason, I do think your chances are definitely the best at Sim Lim or Funan.
That being said, prices of branded electronics are not necessarily cheaper in Singapore compared to Europe as you noticed.