I'm replacing a Dell laptop power supply with an old Mac Mini supply I have laying around. The broken Dell psu outputs 19.5V and 4.6A and the Mac psu supplies 18.5V and 4.6A. I hoping that's close enough and will suffice.
My issue is splicing the Dell cord onto the Mac cord coming out of the Mac psu. The Mac cord simply has a red wire and a black wire, as seen here:
The Dell cord has the outer layer of black rubber, then a layer of wire mesh, surrounding a layer of white rubber, then another layer of wire mesh, then another layer of white rubber, and lastly a thin wire in the middle. Here's a picture. The two wire mesh layers are twisted up.
My question is which is negative and which is positive? Here's a picture of the Dell connector: