Is it more energy efficient to charge a phone/tablet using a desktop/laptop while your computer is being used vs using the charger?
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.
IF you've a high-efficiency charger, then I'd say it's probably more-efficient to use that charger.
The warmer you run your computer, the less-efficient it becomes, & the shorter the lifespan of the hottest chips in it ( this effect shouldn't be significant )
e.g. increasing a CPU by 10Celsius should cut its lifespan in half.
by having more heat-generating-stuff going on in your computer, you impair the cooling of your CPU & GPU ( slightly, probably ), & that may affect your computer's time-to-failure.
The amount of heat this will add to your case is negligible. We're talking 15% waste on a 20W load, so 3W worth of extra heat. And that heat is produced in the PSU.
If the heat is negligible I would assume it should not matter as long as you do not charge while your pc is doing a task that uses up to much resources?