If you format it will it still work in PSP? If you format it you will remove any files that are on the PSP card. Were files on the Card when you last inserted it.How many times has the card been inserted? If I insert a card from my Camera I would not Format with PC I use the Camera to format. You should be sure that Formatting is carried out if possible in the Device the card is to be used for. It is possible to delete files on a card if no longer required rather than formatting but take care with Format compatability between devices.
Is it possible to Backup your PSP card to the PC by copying to a folder,add your new games to the folder. Delete the content on the PSP card and then add the new folder content to the card. You will at least have a good Back-up of files and would be safe from losing your data.I tend to keep 3 copies of my important files.I save a Grandfather a Father and a Son copy. Any new copy becomes a son and the Granfather is deleted etc.
I sounds a bit over the top but is only for valuable files.