The last time I had my A86U do this was a week or two ago when I updated the current Merlin FW and hit "reboot" on the web GUI after it had finished. Then after 15 mins --> no router b/c it had indeed powered itself off. Power button off / on and she booted right up into the new FW. That's all I can add to this discussion. Very strange and very annoying.
FWIW, there were some postings around the power-supply not be sufficient during a boot-cycle and then someone posted a message on another thread that there was a log message indicating that might be related. We glossed over that? FWIW, it is a darm common thing for a PSU to go into protective mode when overloaded and boot times, with USB->SATA/SSD would be peak use. But I'm like you guys, I've rebooted the AC86 across Merlin FW upgrades and it does not do this all the time. Like LD&D, this stuff is sitting behind a high-quality UPS with some Furman AV voltage regulation HW I had unused sitting in stock. So I do not think it's incoming power supply to the ASUS PSU.
I have an single external USB->SATA (UGREEN) to an small SATA SSD attached to handle amtm tooling. I don't suppose that power draw + the AC86 could be enough to tip over some protective measures which cannot be reset without physical intervention? Could the PSU actually be shutdown when we find it this way? IDK.
I'm sure the PSU on these routers is about as cheap as they can make it! If anyone finds a good plug-compatible higher amperage unit which does
not require me to cut the cable off my working ASUS PSU unit, yell. I wish ASUS would use a standard 2.1/2.5mm plug and 12V unit. But I get why the 19V.. lower amperage. Many Laptops use 19-20V for that same reason but that plug size is the PITA b/c it's only ASUS routers.
I also found the STP discussion interesting.
If anyone knows the exact size of the AC86 male pin, wouldn't one of these work?
Found some speces that say
Connector Size: 4.0mm / 1.35mm
Note: I verifed this size on several sites.. and viewed that it is a very small pin, so the 4mm x 1.7mm would NOT be a great fit.
There are comments below that the inner pin may be too small for the first unit so I'd pause. The 2nd unit has varying sizes.. BTW check out the comments in the first link about the ASUS OEM units being a problem...
https://www.amazon.com/dp/B007O24GES/?tag=snbforums-20
or
https://www.amazon.com/FIT-POWER-Adapter-Charger-Monitors-Westinghouse/dp/B078Y9S1MX/ref=sr_1_6_sspa?keywords=ASUS+router+120W+19V+POWER+ul+listed