Ok. Power controller has a full five volts (purple wire). When the power switch is pressed, green wire goes to zero (which it should not because the number should be something above zero. If reporting an exact number, then the defect has been identified.)
When the green wire goes below 0.7 volts, then the power supply should react. It doesn't. So the power supply is defective. Numbers 3.0 and 0 imply which part of the supply is defective. The power on control circuit connected to the green wire is (apparently) drawing too much power. Both the 3 volts and 0 volts on that wire should read higher. Especially zero which should read higher but well below 0.7 volts.
If damage was created by something external, then damaged power on control circuits would be due to a transient via the green wire. Quite unlikely. Such damage cannot be cause by AC mains transients without causing damage to other intermediate circuits - ie the power supply that connects to the purple wire. Most failures are due to manufacturing defects. This appears to be a classic manufacturing defect.
Information from the failed second supply could better refine or confirm what is seen here.
A power on control circuit and power controller are driven (powered) by a supply connected to the purple wire. That supply is apparently OK. Undamaged by transients on AC mains. Power controller maintains purple wire voltage above 2.4 for more than 10 seconds. So the failed power supply is not being ordered off by that power controller. A supply that powers red, orange, and yellow wires is not powering on. The supply that constantly powers circuits even when power is off is undamaged.
To answer another question, notice many parts of that machine are powered even when the computer is off. Therefore power off is not protection from AC main transients. But in your case, the numbers do not suggest that type of damage.
Your AC receptacle is three prongs. So you should have measured voltages between each two prongs with something (ie a heater) also powered from that adjacent duplex outlet. Measurements are most informative when a load exists. Assume the heater draws 10 amps. So your numbers say the receptacle is maybe 150 feet from the breaker box is 12 AWG wire. Or 90 feet from the breaker box if 14 AWG. If the wire is significantly shorter, then some splice in that circuit is not as 'firm' as it should be. Connections are sufficient. One may not be as good as it should be. Again, facts obtained because you provided numbers (although I had to assume the heater current).
If your AC voltage is changing (with relevance), then incandescent bulbs will obviously change intensity. That 'tool' can accurately identify voltage changes. All electronics are perfectly happy even when a bulb dims to 50% intensity. But voltage variations that severe are potentially harmful to motorized appliances (furnace, refrigerator, air conditioner). Your numbers should read within 7% of 120 volts to protect motorized appliances. Electronics do not care since electronics are more robust.
Not listed are voltages to the safety ground prong. If that wire is solidly connected to the breaker box, then nothing on that wire can cause computer failure.
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