Upvote:5
When converting one currency that is not commonly traded outside its country to another such currency, it is common that the calculation is made as if you converted to USD and then converted the USD again even if you never handle the USD. In this case, at least one of the currencies will not be local, and we are supposing that these are not commonly traded outside their countries, so the rate for that one will probably be poor.
In your case, you might be able to get a good INR to USD rate in India but then you will probably get a poor USD to VND rate. Conversely, in Vietnam you might be able to get a good USD to VND rate but a poor INR to USD rate. The solution (assuming the need for cash) is simple: convert INR to USD in India and USD to VND in Vietnam.
Even with GBP, I have found this when travelling far from home. I have travelled in Asia with friends. I brought USD and they brought GBP. Despite my double changing (GBP to USD in the UK before leaving), I typically got more local currency for the same GBP as they did. In the worst case, I got about the same.
However, I have not checked recently as these days I use an ATM which usually beats any cash exchange.
Upvote:6
It might be difficult to get not so common currencies in usual travel agencies and exchanges. You may have to go to a large scale exchange and the rates will be very less (due to less competition).
For Vietnam, the Visa on Arrival fees is collected in USD anyway. So, you don't need any money till you clear the procedures in airport and find an ATM.
I suggest you to use the ATM card and withdraw money overseas. It will be far profitable, as you will get better exchange rates than the brick and mortar stores. Some tips.