While not an oscilloscope, I tested 4 different old ATX motherboards and the in going from ground to the
3.3V rail, they were all around 3.2-3.8 kohmsThe only system that was lower was a non ATX design compaq system from the early 90.s,
the 3.3V rail was at 7.5 ohms (it still worked the last time I used it but have not used it in many years.
I wonder what if you power the device suing the stock power supply but then bypass the 3.3V raiil on the power supply and instead use your other power supply to power that raid, will the device still work?
A power supply can give above it's rated power. (eg I have an old 300 watt power supply that is rated for 11 amps on the 12V rail, but I am pulling at least 40-15 amps from it (though it is running no other load on any of the other rails (I use it to power an old car radio/ sound system since the system can do 200 watts at max volume (connected to 4 speakers, and I can max it out and none of the lights dim on the radio or the amp. (it is a cheap $12 chinese ATX power supply that came with a $20 ATX case that tiger direct was selling (and also had free shipping
)
I have been using it for a while with no problem (I keep it away from anything flammable just in case since I do have it wired up in a sloppy fashion)
(I bet if I wanted, I could push that china power supply even further above it's limit (not sure at which point it would start smoking, but what ever the real limit is, what ever protection it has (if any) has not kicked in yet
)
edit: Pictures yay (has been had been used in a PC for a year back in 2003, then retired until about 2 years ago for use with a speaker system)