Are you working with an attorney? If so, you should talk to them about how to respond. Otherwise, you have to follow the instructions in the letter. If you try to keep it, then it very well could impact your U visa adjudication. M y guess is that once they have received the card, they will return it with a re-issue it with the correct information. My guess is that it will take about a month, but that's just an educated guess because I have never had this happen with one of my cases.
Either go see an attorney or follow the instructions in the letter. I had a client whose green card contained the wrong A-number due to an immigration mix up. We returned the green card and my client received her new card after about 3 months. Good luck.
This information is intended as general information only. This communication does not establish an attorney-client relationship between me and the asker.
This error should not affect your U visa application in any way. When you receive the new EAD with the correct information on it, it may be valid for one year from the date it was issued. It may take several weeks or perhaps a few months to get the new EAD, though I would hope the USCIS would isue it pretty quickly after you return your current one.