[California, USA, regular 110 V power.]
I'm reading the power factor of my "Late 2013" 27-inch iMac using a P3 P4400 Kill-A-Watt. It reads 0.95 when operating normally (60 to 120 W), but when sleeping, even with Power Nap off and power bouncing between 0 & 2 W (to power the USB mouse & keyboard to allow user wakeup) the PF bounces around 0.50. The K-A-W has a low update rate, so it's hard to read with the computer in this state.
If I "Prevent computer from sleeping when display is off", with screen off it draws about 22 W and the PF sits at 0.50.
In both of these cases (just screen off or computer sleeping), an Ikea LED bulb and my 15+ year old Sony ICF-CD831 CD clock radio's LED display flicker. Usually a few seconds between flicks, sometimes at about 3 Hz. The Ikea bulb runs very hot in a non-enclosed fixture. It might be failing and I'll throw it out when I'm done using it as a diagnostic. A GE bulb on the same circuit does not flicker.
As soon as I wake up the computer, the flickering stops.
My house has a 40 year old 100 Ampere Zinsco panel that the landlord's going to replace. There are only 2 20 Amp breakers for all outlets in a 3 bedroom house and some 3 prong outlets don't have the ground connected.
How can poor power factor on the computer cause devices with poor regulation to flicker? Is oxide on circuit breaker contacts a possible contributing factor?
I checked the line voltage with a DMM & saw it dipping from ~120 to under 110 with a 10 W LED bulb switched on giving an ESR of about 165 ohms, but an 1800 W hair dryer caused the same sag, so there doesn't seem to be a simple non-reactive loose wire.
Diagram added: Load A is iMac causing interference, B is clock radio or 10 W LED light fixture being sensitive to that interference. X and Y are the 100 V loads around the house (refrigerator, lights), Z is lumped 220 V loads (stove, clothes dryer). The only way to eliminate X, Y and Z would be to get a 200+ W inverter and battery and run A & B from that in isolation of other loads in my house & neighbors on the other side of the pole transformer & I only have a little 50 W.