I've got a question like that, I won a 50 Euro psn credit card in a raffle and unfortunately my ps was broken so I wanted to ask whether you can get other things with a psn card or is that not possible?
As the name says:
psn → this is only for Psn store
at most you could sell them
The PSN card (Playstation Network) is only intended for the PSN and can only be redeemed there. A payout is not possible.
You can top up your PSN credit with this card, nothing else is possible with it.
If you want to monetize the card, you can sell it, eBay classified ads with Face2Face-Trade are the ideal solution. In any case, you should never send such a card by post and hope that the buyer is honest.