(adsbygoogle = window.adsbygoogle || []).push({}); I decided to buy a psn card since i can't have a credit card,but will it work in Vietnam (yes i live in asia) even if i pick my region in United State ?

If the PS3 account is an American account, then an American PSN card will work

Yes, as long as the account and PSN card are of the same region, you should have no difficulties.

If you are not using the same currency no.
Not sure if vietnam uses the US dollar for the PSN store.

If you made a US account you need a US PSN card

buy any psn card where you live and it will work, simple as that