Monitor breaks (off and on, display flash) when I turn PC off, sometimes fixes itself: how to reliably fix?

I cannot take an effective video, so I will describe what happens to the best of my ability. [This is the monitor I have.](https://www.pcworld.co.uk/gbuk/computing/pc-monitors/pc-monitors/hp-27ea-full-hd-27-ips-led-monitor-10157835-pdt.html) The monitor works fine during normal use. When the PC is turned off, it breaks.

When it breaks it does the following in a cycle:

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1) White power indicator turns on and stays on for several seconds (Screen is off)

2) Display flashes on, sometimes not showing the full picture, and immediately flashes off. When this happens, the power indicator turns off for a second or two with the picture.

3) Repeat (white power indicator turns on, etc).

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Additional Info:

\- the duration of step 1 is longest when not plugged into HDMI, shorter when plugged into HDMI and the computer is off, and shortest when plugged into HDMI and the computer is on.

\- the power adapter that came with the monitor does this but skips the part where the display turns on at all: Its DC output is 12V - 2A. A power cable of the same size but with DC output 12V - .5A as specs causes the bug as described: I have switched to this cable since I consider turning on the display progress. Both power cables are suggested 50-60Hz.

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While this is happening, I can actually log into my computer and use the keyboard to open programs. I can't see what I'm doing, but the computer itself works.

Sometimes it will naturally resolve, but this time it is not resolving. I am studying to be an electrical engineer, and have good experience in computers, so I'm open to truly anything: I have access to tools to do any fix that reddit can think of. Fixing the issue permanently would be ideal, but I will easily settle for a reliable way to resolve this issue, since it only happens when I turn my PC off.

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Really hope this works. If you have anything to add, I can use it!

\-J