Ya, the power supply that comes with it seems to be under current as I slowly upped the current to it with my bench supply until I was able to make it work properly with a typical handset until I finally put a little more than it's rated for.
I don't have a schematic for the thing but to my recolection when I opened it up, it was ok with the changes.
Giver a try, might help BUT some other revisions MIGHT be built differently... so beware of this.
"Recognize, Realize, and Repent"
Fort Erie, ON
Yeah, it might be worthwhile. If a higher current power adapter resolves all the issues, the SPA-112 really wouldn't be all too bad.