Add the card to Amazon account, get PSN digital delivery cards sent to your email.
I tried adding Amazon gift card balance, Amazon didn't show any errors, however the card hasn't been charged yet and my balance obviously hasn't been updated. Order status just says 'Processing'.
Are the cards supposed to be 'activated' or something before being used? Because if that's the case, these guys should make it a point to let us know.
UPDATE: IT WORKED. Even though when I use standard chartered cards, the Amazon balance reloads within 5-10 minutes, this time it took a few hours, got a text at 5 in the morning saying the card had been charged and then an email from Amazon saying your balance has been reloaded.