As per your description of the fault.
If you are willing to inspect the unit up to board level, if have found similar problems in the past on laptops you could have a faulty Diode or a Capacitor.
a Diode only allows for one directional power and once it goes fault it tends to kick back to the power supply unit resulting in a dead power supply unit light or a flickering power supply unit light, as for the capacitor i have found a few faulty ones before that also does kick back to the power supply also resulting in a similar response from the power supply like with the diode.
I hope this help.
This does apply various laptop brands.
I need some help please, I test two PS on this motherboard and both lights on the PS turn OFF automatically, could it be a faulty motherboard?
by Juan Carlos Núñez Duarte