I see you are having issues with you G550 charging.
You mentioned that the light on the charger is lit up but then it suddenly switches Off, and you also mentioned that the charge still has a light but the power is somewhat low despite of a fully lit up charger Light.
Have you tried draining the power from the system?
- Remove the battery and the Charger or AC Adapter as well call it from the G550 then press and hold down the power button for 10-15 seconds to drain power from the system motherboard.
- Once drained connect the AC adapter but do not connect the battery yet, then turn the Laptop ON to see if the system will power ON using the AC adapter/Charger if it powers up then there is no problem with the AC adapter/charger.
- After testing the AC adapter if it is working power down the Laptop doing a normal shut down.
- Once shut down or turned Off insert the Battery back in the Laptop then turn the Laptop ON using the battery only without the AC adapter/charger see if the system will turn ON using the Battery only.
- If the Laptop powers On using the battery alone with out the AC adapter then the battery is most likely working as well on the issue.
- Now power down the Laptop then connect the AC adapter to the Laptop with the Battery in the Laptop as well then turn the system ON again see if the problem will Occur again having the battery and the AC adapter/charger if the Problem happens with both Battery and AC adapter on the Laptop then the problem is the Motherboard, most probably the motherboard is having issues relaying power from the AC adapter to the battery and may be sent to the Depot for repairs.
I suggest that you call Lenovo for further information about your system, if you still have warranty and is still in the one year period then your system will be covered for any repairs needed - you can call @ 1 877 453 6686 for troubleshooting, you will be asked for a serial number Located underneath the Laptop on a small white sticker that states s/n meaning serial number.
I hope that this Helps.
Have a nice day,