Dell XPS 15 L502X power supply question

I’ve had my trust l502x for a few years now and it’s taken a few knocks over the years and fixed up fine. As of a couple of weeks ago I needed to replace the screen, after replacing the screen the laptop powered on fine on battery, however whenever I try to use the charger it’s LED flashes green. The charger is after market but had no problems to date. I’ve taken the laptop to bits and noted the supply only flashes when plugged in to the motherboard. It stays solid if not connected or connected to the laptops connector while it is disconnected from the motherboard but as soon as connected it flashes. Any idea what this could mean? I’d understand a motherboard issue or socket issue if it didn’t work disconnected or on battery only? Any help or advice would be amazing.