It sounds like you might have an issue with power factor correction and be right on the edge of what the UPS can handle - or the 600VA rating of the UPS is "optimistic" or both. The reality is your setup is "on the edge".
600VA is not the same as 600 watts. They would be the same in a DC circuit, but a VA is less then a Watt - how much ...
Laptops typically do not have power supply units (PSU), like desktops. Since laptops are designed to be as light and thin as possible, putting a PSU in the laptop is not feasible. There are some electrical regulation components in the laptop, to make sure the power coming in the correct voltage and amperage. However, laptops PSUs are the "brick" ...
In general, the connections for the floppy disks are not usable as GPIO pins. If you have the exact specification of the chips that drive the floppy, than sometimes you might be able to do something with it, but it is by no means easy or guaranteed to work. So the answer is probably no.
Whether your motherboard has GPIO pins is impossible to know for us. ...
It won’t be a significant amount, but yes it will consume a small amount of electricity even if the machine is off. The battery slowly loses charge and has to be replenished, some chargers have lights on them that use a small amount of energy, etc.
I'd check power chord electrical specs:
Then check laptop electrical specs, they must be the same.
In your case seems the power chord is good to run computer but to run computer and charge at same time.
At work happend to me the same with a Dell that asks 60W DC with attached power chord outputting 45W max.
As you say the computer is working as the kitchen computer, this is not
a healthy environment and may cause the accumulation of dirt that is not
only dust (that is the problem for most office computers).
In case the problem is dirt, such as fatty deposits, on some contacts,
I would recommend a very thorough cleanup of the computer.
Try using isopropyl ...