Lesson Learned...

"It's simple to install yourself", they said.

"Quick installation", they said.

"The easy and affordable alternative to installing a C-wire", they said.

Well, I have to say, NOT my experience!

I had to hire an electrician to install both - $

Both of my Google Nest thermostats worked fine for about a month.

Last weekend my furnace just stopped working.

Plumber called - $$

After testing the system, his assessment was that the furnace pieces and parts were all working as expected.  He suspected the issue was electrical and he suspected the above shown Nest power adapters were the cause.

Electrician called - $

After testing the electrical, he conferred the Nest power adapters were bad and causing the furnace problems, so he removed them.  He then retested the electrical and all was working as expected.

Reinstalled the original thermostats (thankfully I held onto them) and all was, is and still working fine!

I purchased the Nest thermostats at a great sale price but ultimately this was an expensive lesson.  I now have two Nest thermostats sitting on the shelf in my basement, glorified paperweights.