And I learned that 730 watts + 560 watts + 1130 watts (which totals 21 amps) running all on one 20 amp breaker didn't trip it off. Might be a cause for concern there. I forget if anything else was running on that circuit breaker at the time.
That is normal. Circuit breakers are analog mechanical devices they aren't digital switches (20.00000A = on 20.000001A = off). At just above the threshold it will take a while for the breaker to trip sometimes minutes or even hours. At 30A it would trip within seconds but not "instantly". At 40A it would be very fast probably less than a second. At 10,000A it would be in less than an AC cycle.
The entire electrical code is designed to be conservative though. The wiring for 20amp circuit can handle more than 20A. If you use continual loads (like running miner 24/7) you should derate the circuit by 20% (12A on a 15A circuit, 16A on 20A circuit, 24A on a 30A circuit). The reason is that circuits assume a duty cycle. When current is lower the conductor will cool down. An always on circuit is more stressful. You will notice that a 30A Datacenter PDU has a circuit breaker at 24A. The 20% derate is why.
My apartment voltage stays at 115-117 for the most part, and I found the Volt-Amp setting interesting, but measuring in WATTS is the gold standard for current measurement as far as I'm concerned. Until someone gives me a reason to think a VA measurement is more relevant.
You pay for watts. So if you are interested in economicals watts is what matters. For ATX power supplies the power factor is pretty close to 1 so there isn't much difference anyways.
