What is the best cashback credit cards for buying electronic products (such as laptop which cost $1500 etc) at Harvey Norman, Best Denki and PC or IT fairs?

The best card to use will vary depending on where you are buying from since the rewards differ somewhat by merchant. Will answer this from what I have consolidated at www.whatcard.sg

For Best Denki, the best card would be the BOC Family Card since Best Denki is recognised as one of the Selected Merchants by BOC that give 5% cashback (I am excluding the CIMB cards bcos even though the % is high the cap of $20 cashback wouldnt make sense for your large spend). For Harvey Norman, the HSBC Advance with 2.5% cashback may be your best option. You can directly check out www.whatcard.sg to search for other merchants you may be considering! (including online stores such as hachi.tech/Parisilk)