Parts-People has the adapters for the 5558 here. But are you sure about that size. It looks more like the Latitude adapter which is 7.4mm. Look closely at their adapter then compare it to the one you have. Remember that sizes are determined by outside and inside diameter.
[IMAGE]Shows 'correct' supply being clearly too largeInspiron 5558   HI, I am trying to get a friend's older Dell running. He no longer has a power adapter for it, and - oddly - I am having a difficult time finding the correct model. I bought one that was supposed to be correct, but the pin is way too big. All that I find seem to be 4.x mm in size, but this computer is clearly closer to 3.x mm in size.   Help!   Thanks. Dave
Replacement Power Adapter