I've noticed that GAN PD's 100w and 65w adapters output is actually less (both do not charge my laptop) than lenovo 65w charger (the one with a non-detachable usbc cable). Cable does not matter, tried with many of them including ones providing power from other chargers.

It seems totally random, and you cannot rely on watts anymore.

There's a fair number of misleading our outright wrong specs if your buying from amazon or the like. And even if you're buying brand name, the specs can be misleading. They often refer to the maximum output of all the ports, not the maximum output of a port.

So a 100 watt GAN charger might be able to deliver only 65 watts from it's main "laptop" port, but it has two other ports that can do 25 and 10 watts each. Still 100 watts in total, but your laptop will never get it's 100 watts.

Not every brand is as transparent about this, sometimes it's only visible in product marketing images instead of real specs. Real shady.

> Cable does not matter, tried with many of them including ones providing power from other chargers.

That might not necessarily be the right conclusion. My understanding is: almost all USB-C power cables you will enounter day to day support a max current of at most 3A (the most that a cable can signal support for without an emarker). That means that, technically, the highest power USB-PD profile they support is 60W (3A at 20V), and the charger should detect that and not offer the 65W profile, which requires 3.25A.

Maybe some chargers ignore that and offer it anyway, since 3.25A isn't that much more than 3A. For ones that don't and degrade to offering 60W, if a laptop strictly wants 65W, it won't charge off of them.

So it's worth acquiring a cable that specifically supports 5A to try, which is needed for every profile above 60W (and such a cable should support all profiles up to the 240W one, which is 5A*48V).

(I might be mistaken about some of that, it's just what I cobbled together while trying to figure out what chargers work with my extremely-picky-about-power lenovo x1e)

I have a dell laptop that uses a usbc port to charge, but doesn't actually use the PD specification, but a custom one, so my 65w GAN charger falls back to 5v 0.5a and isn't useful at all. I'd bet dollars to donuts that your Lenovo is doing similar shit.