First, to have a common mode noise (leakage), the computer
must have separate incoming and outgoing electrical paths.
Incoming is AC electric. What is the outgoing path?

Second, leakage through a resistance is rare. Leakage
occurs more often through reactive devices. That means the
ohm meter will not measure leakage through components whose
conductivity increases with frequency and voltage. IOW these
leaks would appear as high resistance (notice I did not say
impedance) to the meter.

Third, all appliances have leakage. GFCI trip is not just
from one device. Sometimes it is leakage from numerous devices
combined. And yet the meter would test every device and see
no leakage from any of them.

To put numbers to what was posted - appliances typically
leak less than 150 microamps when working normally. Show me
the meter that will measure this 800 Kilohm or 1 Megohm
resistor? Meter will declare infinite resistance (more than
tens of megohms) when leakage says 'impedance' (not
resistance) is lower.

Not mentioned is the brand name and model of that laptop.
Not mentioned is whether that power brick is from the
manufacturer or from a third party. Not mentioned is whether
a useless power strip protector is being used. I am not sure
whether the power brick is two prong or three - another
critical fact.

But this is certain. Whether the laptop starts up or is
powered constantly, the current coming in one wire will always
equal the current going out the other - if hardware is working
properly. For those two currents to be different, then
current must have another (third) path out of the laptop /
power brick system. So where is that third path? And how
much current in that third path.

Notice - without numbers then one can only speculate. Get
numbers. How much current is in the safety ground wire for
the entire GFCI circuit? Does the laptop cause this problem
when it is the only item on that GFCI circuit? Contrary to
what that meter will say - all appliances have some leakage -
which is why the ohm meter cannot report 'real' amount of
leakage.

chuck wrote:
It is especially troublesome that the GFCI trips only when the laptop is
plugged into the power supply. There is supposed to be substantial
electrical isolation between the so-called "hot" and "cold" grounds
(i.e., between the AC and DC grounds). Unless that isolation (usually an
opto-isolator) is compromised, I can't imagine a mechanism by which the
laptop itself could trip a GFCI, even if it were hanging overboard and
immersed in seawater while connected! Not so for the power supply, of
course.

Larry's theory of a monster-sized common-mode switching noise signal
propagating through the AC lines to trip both GFCI outlets is looking
more attractive. At least that theory supports a mechanism by which
plugging in the laptop causes a GFCI trip: going from no-load to
full-load would cause a change in switching characteristics that might
produce more noise on the line.

20,000 ohms or less of leakage can easily be measured on a DMM and
leaking RF filter capacitors are common. It would be a good idea to
measure leakage with and without the laptop connected to the power supply.

Chuck

w_tom wrote:
All appliances have leakage. Leakage that should be so low
as to not add up to a problem. It is doubtful that laptop is
leaking milliamps on startup. IOW there would be something
else on the circuit leaking so much that just a little laptop
leakage could trip the GFCI.

Unlikely that you will find leakage with the ohm meter.
Try. But eliminating other items from the circuit, then
powering on the laptop will probably provide better
information.

Informative may be a current measurement of that circuit's
ground wire. How much current (in AC milliamps and DC
milliamps) is flowing down that ground wire for various
powered on appliances on that circuit?