OP, so you did not know VOX Amp? I would not say they are underrated, quite few blokes recorded albums with a Vox and they were not so bad. Actually one of them put a delay in front of it and it was gorgeous even without a loop
I think a lot of the boutique brands would qualify as underrated. But, from the ones I've owned, I would say Samamp is at the top of being underrated and innovative. I have the the VSC12 which is a 12-watt 1x12 combo. The innovation in this amp is the use of a 1-watt all tube amp section that feeds into a transistorized power section to drive the speaker to achieve the 12-watts. It's a great amp for home use or a small venue gig. He had other amps using other innovations. Check YouTube for some of his other models.