Also, its quite unreasonable that my charger, that uses 1.5A AC, would
consume 345W and only output 19V * 4.74A = 90.06W
That would be unreasonable but that doesn't happen. The 1.5 A of current is at the lowest AC supply voltage that your charger can tolerate and still work. From what you are saying that sounds like 110V RMS. So now your input power will be 165 watts but that's still sounding a bit high so maybe your charger can operate at the "generally accepted" "world-standard" of 85V to 265V. At 85 volts RMS and 1.5 amps, the input power is 127.5 watts and this is a power efficiency of: -
Power efficiency = 100% x output power / inputted power = 71%.
Also, it is rated above 80% efficiency, which doesn't meet the
If it is rated at above 80% efficiency this may be at the 230V range with efficiency dropping to 71% at the lower end of the range. Or you may have measured the value incorrectly.
Whether DC or AC, instantaneous power is instantaneous voltage x instantanous current. You then find that if you average the instantanous power over time, it becomes real power of which your can be billed for. Here are various scenarios: -
How can I calculate an electric device's power usage given its current
and AC voltage?
If you want to do it accurately you have to use a wattmeter and this gives you true average power - at the heart of any wattmeter is a device that multiplies the waveforms of voltage and current.
These days power supplies like yours are usually what is known as "power factor corrected" but if yours is an older type supply, the current and voltage waveforms may both look very different and not be truly in-phase. That makes simple power estimations problematic.