XPS 8700 Management Engine problem during BIOS update

I had problems updating the BIOS to A14 relating to Intel's management engine, and I found a solution that worked for me.

I can't narrow down the exact item that fixed the issue since I can't recreate the original problem, but basically I downgraded to a fresh Dell Win8 install, installed the Win8 chipset drivers, did a very hard NVRAM reset, and then successfully re-installed BIOS A14.
Then I was able to wipe the drive and install Win10 without any further issues. 

Symptoms:

• BIOS A14 upgrade failed on ME: “Fail to get current ME version, process aborted!”
  (Or when updating from DOS: “Can not get current ME version from log!”)
• Device Manager: Intel management engine “STATUS_DEVICE_POWER_FAILURE (code 10)” error
• Event Viewer: System log showed “Intel(R) Management Engine Interface driver has failed to perform handshake with the Firmware” - source listed as MEIx64
• Slow boot

What didn't work:

• Downgraded BIOS all the way to A06 and attempted incremental upgrades
• Cleared NVRAM by removing battery (the first attempt failed - even though the BIOS did require reconfiguration at POST)

What I did:

• Downgraded to A06 BIOS (note: command-line switch is "/forceit")
• Unplugged network (to prevent any auto driver updates)
• Wiped drive and installed original Win8 OEM install with recovery USB from Dell
• Installed the Win8 “Intel Z87” and “Intel AMT HECI” chipset drivers from Dell’s website
  (In Win8, there was no yellow warning in device manager but I saw a MEIx64 “bus reset” message in event viewer every ~20 seconds. Not fixed yet!)
• Unplugged power (& Ethernet); removed NVRAM battery; held down power button for ~10 sec to drain power; moved PSWD and RTCRST jumpers to other pins; attached power cable for 10 seconds (did not power on); unplugged power; returned jumpers to original positions; attached power & rebooted
• Re-ran A14 BIOS upgrade (with "/forceit" switch). This time, it worked completely!
• Wiped HD and installed a fresh clean Win10. No errors, & using standard MS drivers.