Why I never show my power supply.

I like this power supply, but it's got a huge design flaw. It has three voltage ranges which can be set independently for voltage and current limits in the range of 0-16V @ 5A, 0-27V @ 3A and 0-36V @ 2.2A. When you select a range it stores it in memory and lights an LED to show the range it's in. But occasionally it blips, and when it does it shows no range selected (all LEDs out) and presents the voltage set on the highest range unexpectedly. This is not good for low voltage circuitry. Note that the voltage it was putting out was the one set for the highest range.
The issue seems to affect the same unit under various brands, but this one came from Maplin Electronics in the UK. I do recall seeing an angry review on their website raising this issue which was deleted.
It's a shame as the unit is otherwise very good.
Note that the 39.86V displayed when pressing random buttons was the upper voltage limit, and perfectly normal.
At a wild guess this may be a software issue involving corruption of the file that is used for the two bit setting (four possible values) of the voltage range. When it erroneously selects the one value that doesn't relate to one of the three ranges. That's hinted at by the missing range LED and default output of the voltage selected in the highest range. That suggests a possible safeguard might be to make sure that the other voltage settings are programmed to a safe low level like 3V when not in use.
The most annoying thing about this quirk is that it only happens once in a blue moon. I decided to film it if it happened again, and here's the video of that rare occasion.