Pinecil V2 is specified to be 88w -- less than 100, but not very far off.

And with a (simple) firmware change and the appropriate 28v EPR charger, it can do 140w.

I goofed up. It can do 126w (not 140w) with the appropriate charger.

https://wiki.pine64.org/wiki/Pinecil#Power_Chart

Yes, and your link shows that the power delivered is dependent on tip resistance (which can vary with temperature). Hence pinecil --or almost any other usb-c iron-- cannot control real power delivered.

And you cannot fix this with updates, no firmware can magically grow buck converter with beefy inductor inside the iron...

Yes, and yes. And absolutely not.

The chart is intended to show values for both kinds of tips that are usable on a Pinecil. V2 tips have a lower resistance, by design, and either style can be used with either handle.

Temperature is not indicated, although resistance can vary with temperature. But then: Temperature is never indicated for power of soldering irons. If you want to begin a trend of producing this data and filling this void, then by all means do so. Let me know how I can help.

And no, we absolutely do not need a buck converter to accomplish heating a resistive element in a circuit, nor to use PWM to modulate the average power dissipation of this circuit. (A buck converter can be used; sure! But E=IR and P=IE anyway.)

Sure, P=I²R but only when you control the current. And P=U²/R when you control voltage. But USB-C can only give you 9V, 12V, 15V or 20V (depending on source, several of these steps might be missing), or 28/48V with EPR.

Given that resistance is mostly fixed you cannot reach the maximum rated power, unless your tip is precisely matched for any of these fixed steps. And PWM does not work with some power sources because of sensitive overcurrent protection.

So you're saying that the iFixit iron can reach maximum rated power (100w) from 9v, 12v, 15v, and 20v, and 28v/48v? Or some subset of these?

Or what, exactly? What function does a buck converter serve in this application?

You'll have to spell it out for me, because right now using a buck converter in a portable USB-powered soldering iron sounds like a solution looking for a problem to solve.

Yes, this allows ifixit's iron reach maximum power the supply can provide (usually requesting maximum supported voltage and sinking up to maximum allowed current), regardless of current temperature and/or tip model.

Most of casual users of usb-c irons do not care about it, but if you ever used professional stuff, these usb toys appear to be deficient in comparison.

That all makes sense, but: Isn't a pro likely to be inclined to keep the most correct portable USB brick with their portable soldering iron?

They are universal, after all -- at least downwardly.

And what may be some examples of a "pro" soldering iron that uses a buck converter (or transformer taps or whatever) to be flexible to a variety of input voltages?

Is the reason a buck converter is required so that it can increase I? I = V/R, by increasing V we can increase I?

I suspect the usb-PD standard doesn't allow for raising the voltage any more than they already do

Even if usb PD could go up to over 9000 volts, it can only provide fixed set of voltages, none of which can really match what every tip requires

Actually that's not true anymore, PD Revision 3.1 has an adjustable voltage supply mode that can do any intermediate voltage between 15-48v, with a maximum power of 240W: https://www.usb.org/usb-charger-pd

I don't know how widespread support for that is though.

PD2.0 is here for a decade already, yet many power bricks skip steps between 5v and 20v, so I wouldn't hold my breath here...

PD with EPR can go up to 48V, 28V support is common-ish.