The file userkey.psw has nothing to do with encryption (think PSW = Password Recovery).
The file userkey.psw is what Windows saves on a password reset disk/USB that you make from Control Panel, Users:
If you used Windows to encrypt files/folders on Computer A you would have been prompted to create and save an Encryption Certificate or you can create one manually at any time:
The Encryption Certificate would normally be saved and backed up on a floppy/USB thumb drive or some other removable media:
If you then have a backup of your encrypted files and then reformat Computer A or reinstall Windows on Computer A and restore your backed up encrypted files you will not be able to access them without the Encryption Certificate you made before. If you don't have the original Encryption Certificate you will never be able to access the encrypted files - your data is lost.
If you take Computer B and copy the encrypted files to Computer B you will not be able to access the encrypted files on Computer B without the Encryption Certificate you made on Computer A.
If you do not have the Encryption Certificate from Computer A you will never be able to access the encrypted files - in that case your data is lost.
This is a fairly common problem because folks don't understand how Windows encryption works or don't follow the directions for how to use it
The problem is folks encrypt their files/folders and do not have or keep a copy of the Encryption Certificate from the original system.
Then for some reason they reformat or reinstall Windows, restore their encrypted files/folders or move the encrypted files to another computer and can't access them.
The encrypted files/folders can't be accessed because they don't have the Encryption Certificate from the original installation - in that case the data is lost.
MS TechNet sums it up
By far, the most frequent problem with EFS occurs when EFS encryption keys and/or recovery keys aren't archived. If keys aren't backed up, they cannot be replaced when lost. If keys cannot be used or replaced, data can be lost. If Windows is reinstalled (perhaps as the result of a disk crash) the keys are destroyed. If a user's profile is damaged, then keys are destroyed. In these, or in any other cases in which keys are damaged or lost and backup keys are unavailable, then encrypted files cannot be decrypted. The encryption keys are bound to the user account, and a new iteration of the operating system means new user accounts. A new user profile means new user keys. If keys are archived, or exported, they can be imported to a new account. If a revocation agent for the files exists, then that account can be used to recover the files. However, in many cases in which keys are destroyed, both user and revocation keys are absent and there is no backup, resulting in lost data.