East Tester sells cheap (~USD220 delivered to USA) programmable DC electronic loads. The ET5411 is their high-voltage model (500V max). I bought it to test out vacuum tube guitar amplifier power supplies, also USB chargers, wall warts, etc.
The screen is bright and clear but the fonts are unnecessarily small. The user interface is clunky.
The fan runs on low (pretty bearable sound level) until you hit 90W and then it runs on high (loud) until a minute or so after you drop below some threshold (maybe 90W?).
Build quality is pretty cheap, and like all cheap test equipment, you should take it apart before you turn it on to make sure there are no loose pieces and that all of the power lines go to the right places and the grounds are good. The grounds go from the IEC plug to the chassis/tranny frame and then from the other side of the tranny frame up to the top power-MOSFET PCB. Well, the connections were not good because from the ground line on the IEC plug to where the ground connects to the top PCB there was 6 kOhm.
I think the issue is the thick clear lacquer on the tranny frame and, ultimately, (for you "five whys" / Kaizen / lean / Six Sigma fans) a lack of concern by the manufacturer. I replaced the M4 screws and nuts with better hardware and several interior-toothed lock washers to bite through the lacquer / powder coat. I measured again and the PCB ground line to IEC plug resistance dropped to 0.1 Ohms. I could have sworn that I measured input-level DC on the main heat sink (relative to earth ground) before I fixed the ground connections, but I couldn't get even one volt afterwards.
The power switch is a real disconnecting switch, and it switches the line (hot) input. Strangely, the fuse is on the neutral, so after blowing, the unit will still be energized until the power switch is pressed or the IEC cable is disconnected.
My most powerful (working) DC power supply only puts out 60V @ 3A (I've got more broken ones on the way soon).
NOTES:
I used two M4 Kep nuts (use a 7mm wrench), four internally-toothed lock-washers and two M4x12 screws to remount the transformer and chassis grounds.
Firmware: 1.02.2045.030
Front panel PCB is dated 2019.06.21
High V range (the reason why you would buy this model):
Imax: 3.1A
Vmax: 510V
Pmax: 420W
High I range:
Imax: 16A
Vmax: 21V
Pmax: 420W
Fan is blows through heatsink front->back
Heatsinks are isolated from case by thin fiberglass supports in front and a plastic holder in back.
Banana jacks seem very OK.
There is a top PCB with 3 power MOSFETS and a 32-bit ARM, a bottom PCB with 3 power MOSFETS, and the front panel PCB with a 32-bit ARM.
Top and bottom PCBs are mounted to heatsinks with 3mm brass standoffs.
Six IRFPF50 power MOSFETs (3 on top PCB, 3 on bottom PCB). These do not use mica or silpads, just thermal grease.
Displayed amps matches my Fluke 179 very closely at 1A, 2A, and 3A.
Displayed volts matches my Fluke 179 very closely when unit is not sinking power.
Indicated volts drops a little low when sinking power.
PM me if you want me to take more pictures or test anything.
EDIT:
Related ET54xx threads:
https://www.eevblog.com/forum/testgear/et5410-electronic-load-mod-add-external-sense/ (might work for ET5411 as the hardware looks similar)
https://www.eevblog.com/forum/testgear/et5410-or-dcl6104-or-a-third-programmable-electronic-dc-load-in-the-budget-cat/ (posted spec sheet for ET54xx DC electronic loads)
https://www.eevblog.com/forum/testgear/et5410-electronic-load-cccv-and-cccr-modes-what-do-they-do/ (What are CC+CV and CC+CR modes?)
https://www.eevblog.com/forum/testgear/program-that-can-log-from-many-multimeters/ (Datalogging application that might work with ET54xx-series DC electronic loads)
https://www.eevblog.com/forum/testgear/cheap-dc-load/ (discussion about various cheap DC loads)
There are others. Use the search