That 3 wire problem , not a problem. Have the compaq with me now , took dvm readings, chassis ground to outer face of that 3 way line connector, red DVM plus probe to chassis on diode test 0.63V forward V, nothing on neg to ground . Current limited power up on bench supply, needed to switch on pc before it would charge (maybe my inadequate bodged up dummy 7.3/5mm connector). No requirement to have third pin connected for this use. No popup my side of Vista password entry anyway, perhaps a Dell problem and third wire problems.