I think the difference is the power brick probably doesn't allow the +5 and +12 to decay at the same rate. That must affect whatever logic they used to determine that they had a loss of power while operating. Remember, it has to also handle the situation where the device has been turned off normally, then unplugged and plugged back in. In that case, I suspect they don't want the NAS to power up automatically. I know I've done stuff like this with avionics, but I actually had hardware assist designed in to make the job easy. I'm not sure how they did this in the DNS-321, or what hardware support they had available to determine that they were operating when power was lost. Since they can't really spin up the disks to decide whether to power up, I suspect they write an "operating" flag to the FLASH when they're running and clear it when they're powered down normally, but that's just a SWAG.