My Chromecast Ultra comes up with the warning that it won't stream 4k because of a 'non-standard power supply'. I'm using the out-of-the-box power supply. If I unplug and re-plug the power supply it will work for a short time but go back to displaying the warning.
I appreciate your help here, JillG.
vontonks, hope that helps but if you're still experiencing the same issue, you may also plug in the Chromecast into a different HDMI port on your TV and try to update your TV's firmware, if possible. Feel free to let us know if you still need help.