Precision 5550, broken replacement motherboard?

Hi, this is a very unfortunate series of events and I'm really sad and angry about the situation. The machine is a DELL Mobile Precision 5550 with latest bios and drivers (verified with DELL update utility).

Last year august my SSD went bad and I contacted the DELL assistance about it. With all the problem by the DELL assistance in bisecting the problem and me saying multiple times that it was the SSD broken, in a span of a month they manage to:

- Replace the motherboard (the motherboard was fully working and didn't had a problem)

- Finally replace the SSD after me contacting them again that the problem was still there

- Come again to fix broken speaker as something went bad in the motherboard replacement in point 1.

Things went good for a month but I started to notice some problem with charging. I hoped it was the cable so I didn't care to contact assistance again given the unreal waiting time (I had next-day assistance and took them 1+ month to fix the problem) as I didn't want to get mad again.

Problem went even worse so I decided to contact assistance again. My usual luck, without noticing, I contacted them exactly one day before warranty expired. I contacted them around 3:00 PM. They answered at 5:30 PM that it was too late and they would take the ticket the next day. And the next day, surprise surprise they answer with "The warranty has expired". With my great joy of discovering this as the website didn't give clear information on the day of expiration but just the month, I was shocked.

Next some month with this problem that was annoying but not that problematic we reach today.

The problem I suffer:

- PC turn OFF instantly at random times. In a timeframe of 30 minutes it did turn OFF 3 times at random times. Instant. No blue screen nothing.

- After the PC turn off, the power charger is not detected, the light is off, the PC when Windows boots warns "The Pc is not in charge, Attach the original Charging Power adapter". (but the original charger adapter is correctly plugged in)

- To exit this glitch, I have to power cycle the machine, detach the power cable, wait some seconds and attach the cable again. Only now the white light turn ON and the PC starts to charge.

What I tried with no success:

- Reinstall Windows

- Change the power adapter with a new one

- Replace the battery

- Reset the BIOS

Still the same problems. I can only think at this point that the technichan replaced my working motherboard with a defective one. I remember at times him saying that it could have been a repaired one. If it's useful the sticker on the motherboard are white instead of the usuall yellow.

The thing is not usable, with the power cable attached the problem is less present but still happen sometimes. I wasted lots of money on this PC and brought the Precision variant to have a stable machine and the thing just turn OFF randomly making me lost all my current work.

I honestly hope anyone can help me with this since it's really impossible to have one correctly working motherboard being replaced by a faulty one.