I use a CashPlus prepaid Mastercard all over the world (including Thailand, Singapore, Malaysia, Korea, HK, Australia, NZ) and have had no problems with it at all. There is a standard fee of, I think, 1.5% for foreign currency transactions on this card, but that's pretty standard. You can use it in ATMs as well. If you are travelling to the USA or Europe, they also do US$ and Euro cards where you then don't get charged the foreign currency fee because it's in the right currency to start with. You can load them at the usual places and they have a freephone line and have always been really helpful when I've called.
Either way, enjoy your trip!