If it won't boot, that could be lots of different issues. So before you go too far, try running the PSU BIST tests. Don't know if this model has a BIST button on back of the PC or not, but there are instructions for testing models with/without that button, here. And read this and this about replacement PSUs for the Inspiron 5680. BTW: If the PC is connected to a power strip or surge protector, remove those and connect PC directly to a working wall outlet. And then try to boot, while watching the power button on front of PC. What color and is it steady or blinking? If blinking, count the blinks which is an error code.
I am trying to fix a Inspiron 5680 for my grandson. It appears the power supply is bad based on what he has told me. I haven;t actually had a chance to look at it yet. Does anyone  know the part number for the power supply. I looked at he device details online with the service tag, but can't figure out what part number is the pwoer supply
Inspiron 5680