What you're probably seeing is not three traces melted together. Sometimes during the pcb creation process, that happens. . . for stability of the product, supposedly.
If you're scared of blowing a fuse, then skip the testing phase and look straight at where the power cable receptacle meets the PCB. There are two "bolts" that are soldered to hold the receptacle onto the board. Resolder those. And then resolder the two tabs that meet the PCB (the ones that actually lead to the power cable receptacle).
I know that this isn't the only problem that power supplies, but the sizzling thing can be narrowed down easily in a darkened room. NOT DARK. . . just darkened. When you give power to the PSU, you will instantly see where the arking is occuring. It's handy to have everything plugged into a surge protector with a switch. That way you can safely turn off the current as needed.