Manfred, Sorry about mis-spelling of your name. My typing is pretty bad, and I don't always see my mistakes when the character echoes are delayed over my sometimes problematic and always slow dial-up line. Now as to the power supply thing, I've tested a number of supplies from various vendors by intentionally shorting out the +12 to +5 lines while the system is on, and what usually happens is the power supply trips some kind of protection. In all cases, the +5 supply has much greater current capacity, and thus much less internal impedance, so it will bring down the +12 supply, causing an overload, and trip the +12 supply protector. Most will come back on as soon as I remove the short, but some required unplugging the line cord to reset, and a couple blew their internal fuses. I've yet to burn out any components on the motherboard doing this test ("so far so good"). Along this line, shorting out the +5 line to ground can cause a lot of fireworks, as the +5 supply usually has the most current capacity, so it will not trip unless its limit is exceeded. For example, even a 180 watt power supply will have about 30 amps on the +5 supply, and that's enough to burn out small wires without tripping the protection. I agree that if the power supply does not have adequate protection, it is possible to apply +12 volts to +5 volt devices if the fan connected across them should develop an internal short, but I think most modern power supplies must be protected from these events; the +12 traces on most circuit boards are just too close to the +5 traces to assume that no one will ever accidentally short them out. Now you have me thinking about the next test: put a fan across the two supplies and jam it so it can not turn, and see if the power supply will burn it out to an open circuit or turn it into slag that forms a short circuit. eyc