OK I am at my computer now. Continue from previous thread on the extra charge/fee.

The extra charge/fee is what~
MasterCard calls it "Cross border transaction fee”;
Visa calls it “International Service Assessment (ISA) fee”
and usually it is around 0.15% to 1% (I noticed so far Malaysia issuing banks go for 0.8%) from the total transaction.
Do note though it is Visa/MasterCard that applies the fee to the issuing bank and in turn, depending good or bad bank, either they absorb the fee or offset it to you (worse, they mark-up).

Refering to one example from limjenson:
Bought Shadow Warrior at 7.50 and SMS said RM 7.50.
Statement arrived, was charged 7.56 (7.50+0.8%).

Thread below is a good read. I copied some info from it.
https://forum.lowyat.net/topic/2519936/all
Visa and MasterCard now charge a cross border transaction fee even when no currency conversion occurs. This relatively new fee - “cross border transaction fee” (MC) or “International Service Assessment (ISA) fee” (Visa) – was initiated by Visa and MC to ‘fight’ usage of the international credit card processing network when no currency conversion occurs.

You may ask what kind of condition you will be charged with this fee and what's the difference if you buy online in foreign currency?
Simply put:
If buy in RM (local currency), but merchant's gateway/payment system in foreign country = Charge cross border transaction fee.
If buy in foreign currency = Charge with bank's conversion rate + admin fee (depending on banks)

So to know if your bank(s) has been "quietly" charging you with this fee all this while:
Check your online/paper statements for the charged amount on POSTING DATE and compare it to your Steam invoice/receipt or the SMS notification.
If they are the same, good for you - keep the card.
0.8% fee is easy to miss but it is noticeable if you spend a lot.

TL;DR - Banks which don't charge cross border transaction fee (copied from lowyat CC thread above). Go with these for your next Steam purchase:
+ OCBC
+ Maybank
+ Ambank
+ UOB
+ Alliance
+ Citibank
+ Public Bank

Cards that you should avoid if you plan to use it for only Steam purchases:
- CIMB

(**However do research the cards reward/rebate. It may be rewarding for you based on your spending pattern in the long run although it sucks with the fee**)

Would be great if other people can check their statements and feedback here if they were charged with cross border transaction fee, or not. Quite valuable info and I plan to update the list of banks with the info.

Feel free to correct me if there is any wrong information.