PS Vita: UMD Conversion Utility
It's an app you install on your PSP, and have it check to see if your UMD is supported by the digital copy. This is a hit or miss, even if there is a digital copy available. If found, it provides a discount on the digital copy on the PSN store. For the two UMDs I have that actually supported this, the price was 500 yen each. If you had a recent game, I'm not sure what the price would be then.
So it's not actually a fee but you are buying another copy of the game at a greatly reduced price.
For games you don't have yet, it's cheaper to simply buy any game you want already on the PSN store, even if it means you have to order a PSN Japan card, rather than going through the conversion (unless you get the UMD for really cheap). If the game has an English version, you might rather go with that instead of converting. Of course, doing all this requires that you have a PSN Japan account and that it's activated on your PSP (so you can't be using your English account on it).\
If the PSN USA service ends up like this.... well, we'll see.
So it's not actually a fee but you are buying another copy of the game at a greatly reduced price.
For games you don't have yet, it's cheaper to simply buy any game you want already on the PSN store, even if it means you have to order a PSN Japan card, rather than going through the conversion (unless you get the UMD for really cheap). If the game has an English version, you might rather go with that instead of converting. Of course, doing all this requires that you have a PSN Japan account and that it's activated on your PSP (so you can't be using your English account on it).\
If the PSN USA service ends up like this.... well, we'll see.