S2718H, doesnt recognise original power adapter

Unfortunately, yesterday I stumbled upon my first issue with monitor S2718H 27". I turned it on and the message on the screen was "Please use the power adapter that came with your S2718H/HX". At first, I found the solution: unplug all cords, hold the power button for 8 seconds, then plug-in power cable and turn it on -  it worked! I did a factory reset too just to make sure.
But today these steps aren't doing the trick anymore no matter how many times I tried! It still grumbles that I'm using the wrong power adapter.
My warranty is still active. I guess the power adapter or monitor itself needs repair or replacement? There is another thing that concerns me. I bought it from Amazon in the UK then moved to the EU country, Latvia. I understand that I have to do ownership transfer BUT before that here's what bothers me - I can't find any information on official Dell services and repair in this country, like where am I supposed to bring/send my monitor to.