My thought was that given the small number of shares, the dividend would also have been a small amount and would have gotten lost/forgotten in a move.
Having the SSN on the account will help with Xcel Energy Investor Relations, share transfer, and dividend recovery.
To transfer the shares into your name, you'll need a Signature Guarantee which can be done at your local bank branch once you have the physical shares, and proof that you are over 18/21.
Unclaimed dividends would have been sent to the last registered state's unclaimed funds. So if your parents did update the custodial bank you'll have to look at that state and any other state as well. Fortunately most/all? states have a online unclaimed funds page for searching.
Since Wisconsin is on the title, you can try to see if your name or your father's name shows up here. Don't forget to try out variations on the full certificate title in the search fields.
https://www.revenue.wi.gov/Pages/UnclaimedProperty/Home.aspx
Good luck.