Amazing, but this makes my head hurt. Only reason I can figure that this works is that the voltage coming off the charge controller is probably like 13.7v as it's trying to bulk charge or something, and the PSU is probably shunting above 12.5v. When the solar charge voltage drops below 12.5v the psu starts trying to hold at 12v.
I don't love it, would prefer the logic in a single device, especially if the psu is tied to mains. That being said, if it works its not stupid, and this is genuenly one of the most intersting thing I've seen recently. Congrats!