Is it be advisable to apply for a credit card from a different company with better cash back rates (BOC/UOB) and then paying off the credit with my DBS credit card (so i get both the cash back from and multiplier)?

@Quick Draw Can you help me solve this problem? It makes sense to me actually to charge to other credit cards to optimise returns.

Yes to getting other banks cards for better cashback. No to your 2nd part. Paying other banks credit card bill, or paying for the same bank credit cards is excluded from getting rewards/points/cashback and they do not count towards pushing your Multiplier to a higher tier of interest.

Repayments are actually excluded from cashback/rewards schemes.

Only spendings will get you these rebates.

Have to check the MCC codes to see if it's excluded.