Funds in your online wallet are used to pay for PlayStation®Store purchases. You can add funds to your wallet using a credit card or PlayStation®Network card.
In the PlayStation®Store, you can download (as a purchase or for free) products such as games, additional items for games or video content.
On the XMB, there is a category called "Account Mangement".
Next, you go to "Transaction Management".
After that, you go to "Transfer Wallet".
Once you are in there, you'll have two options; Credit card or PlayStation Network card.
(If you have a credit card, proceed by choosing "Credit card" and enter in your card information.
If you have a PlayStation Network card, proceed by choosing "PlayStation Network card" and enter in the code.
You'll also have the option to choose a amount of funds you want in the "wallet" for the PSN store.
If I recall correctly, the store is strict (lol).
By strict I mean that you have like three amounts you can choose from.
I think I am wrong right there, but just go ahead and check it out.
You should now have funds in your "wallet" so you can purchase whatever the PSN store offers.
This is probably a stupid question, but is there a way to add funds to your wallet online rather than through the ps3? The PS3 wont update my credit card info