For the AC-DC Power Supply with 1.7mm Barrel, you can find cheap ones on eBay, 5VDC 2A, around US$3.00 each.
If you don't want to tweak the "dvfs" table yourself, you can also run a simple script at boot up which reduce the CPU frequency.
I've done that on my to OrangePi-PC, and there are stable since several weeks.
So, I've decide to order some more :-)