In a nutshell, most likely overhyped and definitely underperforming. We as Americans, all of us, so much want to get "such a deal" and the Chinese play into that American weakness: Almost a deal but not quite the one we wanted
The supply never produced 300VDC but did hold at 280VDC all the way up to 70 MA of current draw. That 20-volt difference at 0.3 amps is 6 watts of power you won't see going into the 12GE5.
Shame on me as two of the comments on the product did spell out that deficiency, yet the supply has a high rating. Certainly not from me! How could I be so blind! Dire Straits said it best: Something for Nothing (But the Chicks are Free... BUT No Freebies Here). This supply might be a $1.25 Hooker disguised to look $2.50.
I did test this power supply on a CW transmitter to see how it holds up. It did OK with a 6L6 in the socket, where we saw 60 MA of Cathode current, and the Drake Wattmeter said 7 watts in 40M. I attribute the puny output to the lower Plate Voltage at 280VDC but with say 350 VDC or more on the plate I could conceivably see about 20 Watts output. (Do the math as 70X0.3 = 21 watts more input at a higher plate voltage.) The signal sounded clean and that was both the case on 7030 and 7060 kHz.
While my earlier tests (in the video) gave pause for the use of the supply on the Hybrid wireless, the CW tests suggest that it may possibly function on SSB in the Hybrid Wireless. That will have to be tested, but it is a disappointment that you can't get 300VDC out of the supply as advertised.
Them that know sometimes get fooled by the bright shiny object. I included some shots in the video of how I built the test fixture. The Manual Mill is sure a handy tool.
73's
Pete N6QW