I was just thinking if you are on your computer anyway would it just use some of the excess electricity that your computer would have wasted or would it be worse than charging your phone from a charger while using your laptop separately.
I was just thinking if you are on your computer anyway would it just use some of the excess electricity that your computer would have wasted or would it be worse than charging your phone from a charger while using your laptop separately.
Gallium Nitride based modern phone chargers are 95% efficient.
The very best, most expensive PC power supplies on 115v AC will only reach 94% at the very specific 50% load of power supply rated wattage. So if you have a 500 watt power supply, and aren’t using almost exactly 250 watts, you aren’t getting that 94% efficiency. Regular power supplies under normal variable load conditions are going to be somewhere in the 80% efficient range. If the PC is idle, that efficiency can drop to 20% (but it’s fine because it’s only a few watts).
https://forum.level1techs.com/t/super-high-efficiency-300-400w-psu/184589/2
So using a modern Gallium Nitride stand alone charger will be more efficient. It will be extremely more efficient if you use that stand alone charger instead of charging off your PC while your PC is idle.
Counter point. Most computer power supplies have a curve to their charging efficiency (somewhere north of 50% load). If your PC is substantially below the peak of that curve, then adding load (the phone) could raise the PSU’s efficiency say from 80 to 85% (I’m making up numbers) which would affect the overall efficiency of the entire PC’s load.
I think your answer is still probably correct, but it’s an interesting nuance to think about.
Side notes: Some PSU’s use gallium, e.g., Corsair ax1600i, though by and large most do not. Also if your in the EU then your working with 220/240v PSU’s which adds more efficiency, but that would apply to the phone charger as well.
Adding a 30 watt phone is going to be maybe 5% of the PC load. So it could bring it up to a few percent. But that is insignificant compared to the normal swings of 200+ watts between normal and load.