the fee for the visa is always in the country where the consulate/embassy is located, here in Canada it’s in Canadian dollars, in Vietnam it would be in Vietnamese dong or possibly USD, it’s up to every consulate/embassy to decide what they will take, most are going to online only soon, maybe all of them are going online soon, you won’t even be able to go into an office at the end of October I read, then I assume you will be able to use a credit card
You start off by saying everything went really smooth, and I guess as far as the visa getting approved at the consulate/Embassy everything was smooth, but forcing you to pay cash only is pure insanity in this world, I use md my visa online at the consulate in Vancouver Canada, it was so easy and so painless, I didn’t have any difficulties. Once I switched to soft power category, I originally applied for a remote worker, I’m self-employed and that was a big problem, but they were so easy to deal with in Vancouver Canada at the consulate, they simply switched my category to soft power, and I provided an estimate from my dentist in Hua Hin for work that I needed to get done. Anyway, I was approved the same day I applied, the next day I applied for my wife and was approved. Bringing 110 bills in cash to a consulate/embassy is a little bit ridiculous 
I actually agree with this, I think Thailand is very smart, they don’t want people with very little finances coming into the country, they become a burden in one way or another, and they certainly don’t contribute to the economy of the country