What are you even talking about? I never mentioned anything about being plugged in. And being plugged in has noting to do with it.
I've tried thin and light machines - anything from ultra low power 15W i7's to the 14" 8 core Asus ROG Zephirus - compared to a workstation or gaming laptop performance is a noticeably reduced. Even in the case of "performance" (notice the quotes) oriented t&l machines, there is simply not enough thermal headroom and power circuitry to enable any serious computing*.
I'll give an example - take the HP x360 - at 15W ryzen 3750h will perform significantly worse then the same CPU but with a higher power limit - 65W like in the Asus TUF gaming. You can add as much ram to that as you want, it's still a dumpster fire.
*And by serious computing I'm talking rendering, compiling and so on - tasks that would benefit from having large amounts of ram. I've seen this kind of talk back in the 2000's - MORE RAM IZ MOAR POWR!!!! - marketing BS designed to make people pay for stuff they don't need. For every day computing 8GB is more then enough. In fact, the PC I use to study and write research papers on is an ancient i7 950 with only 6GB of ram, and it's excellent. Not even having dozens of tabs in edge open at the same time while doing image optimization and OCR in Acrobat DC will slow it down. I've been thinking of upgrading this PC as it's been in use since my collage days, but it's been running so well for the tasks it's expected to do that I feel no need to do so, and it has all the software I'm used to on it, as well as all my research papers and materials from studies and whatnot, so instead of throwing more ram at it or swapping it out for a newer gen machine I simply installed a PCI-E USB 3.1 card and upgraded the CPU cooler.
I brought this PC up because it has about the same performance level as a modern quad core thin and light laptop running a modern i5 or ryzen 5 "U" skew CPU - and 6Gb is not a hindrance. It it were I would have dug into my box 'o' ram and installed an additional 6 GB.
Also I formulated my reply as a serious valid QUESTION - what do you need that much ram for? I'm still waiting for an answer. I gave you a practical example of using 6Gb in 2022 for Acrobat DC, image recognition, OCR, photoshop, document digitalization and on line research (witch often involves having over 50 open browser tabs or multiple browser instances running at the same time) with no slowdowns or other issues.