|Keep to the old RAM for now as we know that used to work. Clean its edge connectors with a soft pencil eraser and pop the old RAM stick(s) in and out a few times to ensure the sockets are clean. Sometimes it can be due to a minute amount of oxide if the RAM is in the slightest different position.|
If that doesn't help and there is more than one RAM stick, try each one on its own in each of the positions previously used.
If necessary, check all connections around the RAM area that might have been disturbed (remove and re-insert).
The charger is a possible culprit but it's hard to see why it was related to anything you've done, provided it is plugged in firmly.
Always pop back and let us know the outcome - thanks