I finally find out the detail about the charging mechanism that cause the problems we have encountered.
First of all,
@Whitigir and
@davidmolliere are right, the problem is a protection mechanism triggered by the temperature of the N8ii. When the N8ii power management software detected a higher than normal operation temperatue, it will try to do something to lower the temperature and among that, disconnecting the charging current is one of them. The trigger point of this protection mechanism is 50 degree C. The power management software will monitor the internal temperature continuously, when the temperature drop below the safety margin, it will resume charging. So you don't need to disconnect the charger from N8ii to trigger the charging handshake again.
Both Class A and P+ might present a high risk to trigger the protection mechanism when you charge and playback at the same time, especially when you playback high sampling file or driving a demanding load. Tube or Solid State is not as significant when compare to Class A or P+. I have conduct a
charging test with Class A earlier on, but since I didn't put on the leather case, the temperature of N8ii has barely escaped the protection mechanism. If you must charge and playback at the same time, stick with Class AB in standard P mode, or improve the ventalation of your N8ii, be reminded the N8ii chassis is a big piece of heat zink to the circuitry in the DAP, So its like adding a fan to the heat zink of your CPU to make sure the system can remain efficent even at high temperature.
Having said that, even when you are not charging and playback at the same time, you still need to be aware of the protection mechanism. The N8ii can can reach 50 degree C if you put the DAP in a small consealed unventilated space (such as your backpack) and playback in demainding settings such as Class A and P+ mode. Ultimately when the power management software has tried all options but the temperature continues to rise, it will shut down the player.
Since we are on the topic of charging, I would like to confirm that N8ii supports PD and QC3.0 fast charging protocol. It will consume up to 18W charging only, so a 30W or 60W PD/QC3.0 charger will not charge it any faster beyond 18W charging capacities. These high power USB charge are benefited when you need to charge multiple devices at the same time.
I'll include this in the
N8ii FAQ at page 1, hopefully this will steer users away from similar problem.