It's an interesting concept, but it's got issues where powering synths is concerned. The docs note the power in watts, from which I did some calculation, and all but the stronger (and more exotic) PoE versions would only be able to power more than a basic skiff. Also, whatever case would be connected would need power for the +12, -12, and 5V rails, which means there would be some loss due to the DC conversions necessary...on top of some inherent issues in some of the PoE formats where they also involve some current loss...such as 90 watts in the "supply" end, which equals a drop over the system of around 20 watts, leaving only 70-ish watts at the "business" end. And while 71 watts does equal 5196 mA (@ 12v), that would still have to be split by the synth's P/S into the three different DC rails, which equals further losses due to both conversion and thermal issues. In the end, those loss factors don't bode well.
Now, what I would much rather see is a DC supply that ties in with the synth's DC rails via Anderson PowerPole connectors, only utilizing a voltage converter in the cab for the voltage changes. ADDAC does something like this for their huge 1 meter cabs, although some of their designs still utilize a single DC input for the power supply to split, and Konstant Labs has a similar P/S chaining protocol (with Molex connectors). But if we can go to something like, say, THIS: https://www.dxengineering.com/parts/asr-rs-35a-ap ...well, given that it's a linear supply, it would be DEAD-quiet on the DC rails even with the necessary voltage conversion done inside the cab. And at 35 AMPS, loss factors stop being a problem. If we had something along THOSE lines serving as a single DC source, and the voltage conversion wasn't current-limited at a low level, that's where we should go, I think. Plus, with the right voltage conversion, the external P/S could be the determinant on maximum deliverable current, and NOT an internal supply. This would also reduce in-case heat factors, too.