i would get a inductive current meter, here you can buy them for like 7 or 8 bucks at harbor freight.open your Breaker box and see how much current is flowing through the breaker your on, maybe half the house is on one breaker?

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That won't really tell you much, since we know it isn't overcurrent causing the trip. If the Mac were drawing enough current to trip the branch circuit, the power cord would be getting hot. It has to be leakage current from hot to ground, bypassing neutral, and it's probably only a few mA, far too little to measure with a clamp meter.