That “power supply” could also be another 12 volt boat battery as well.
If different electrical connections do not help, I would than try loading an older version of software onto the unit.
If you knew someone with the PC Connect cables than you could possibly download the waypoints your unit has on it now. If you do have to send the unit into Humminbird, the standard procedure is for the Tech to try and download your waypoints first before trying to repair it. They get loaded back on after any repairs are made or if your unit has to be replaced. However, there is the chance that this is not always possible so it is wise to always keep an updated copy of your waypoints on your computer.