I wouldn't flash it right away. Since the same PSU works with other units, I'd start with a factory reset and set up the pool again. If it still reports an incompatible power adapter, then check the firmware version and contact Canaan. Flashing it too soon may only make the fault harder to isolate.
Already tried a reset - and already contacted Canaan they told me to go pound sand, the warranty is expired. I am going to do a reflash of the FW this weekend. The miner was working up to the point where I changed the pool info. I changed it on all of my nano's at the same time, this is the only one that had any issue.
Reflashing the firmware won't help if there are faulty components on the board.
You need to examine the power circuitry, though there aren't many parts there that are prone to failure. You should start by replacing the connector, then check the voltage at the inductors and the controller- or do it the other way around if the connector is actually fine.
I am aware that if there are bad components inside that flashing the firmware wont help. I have already opened it and the connector looks fine, it is not loose. There are no parts that look damaged or "blown" so before I start removing or replacing the connectors and parts inside - I will attempt reflashing the firmware first.