This reminds of me a funny/annoying thing I had happen to me.
A few years back, I bought a Dell laptop that was under their "workstation" line. Dell Precision 7520. The default config when ordering these was had a power-hungry nVidia GPU on a dedicated card. I customized the laptop upon ordering to remove the GPU since I wasn't going to be doing anything that needed a GPU. (I just wanted lots of ports, a nice keyboard, and a touchpad with three buttons. Thinkpad was not an option at the time for reasons.)
Unfortunately, the 7520 firmware was hardcoded with power requirements for a fully-loaded system. It came with a big 180-watt brick. I knew that the laptop wasn't going to need that much power, so I would occasionally use a 90W Dell power brick that I had laying around. I turned off the boot-time warning about an undersized power brick, reasoning that if the battery started draining while plugged in, then I would give up and switch to the bigger brick. The battery never drained.
What did happen, though, is that sometimes I would notice that certain UI things were really, really slow. I always ran a lightweight Linux desktop on the laptop, so generally the web browser was the only thing that would cause any serious CPU or memory usage. For the longest time, I just put up with the occasional slowness on big heavy drunk-with-UX-power websites.
Eventually, I got to wondering what was wrong with this laptop that made it _feel_ so much slower _sometimes_ than any other Linux system I dealt with on a daily basis. One day, after working on the couch for a bit in the morning (on battery), I went back to my desk and plugged into the AC and noticed that Slack got _very_ slow. And so did a few other things. Undock the laptop, and things were fast again. Huh, I thought. That's weird. Nothing in the kernel logs or system journal but when I happened to look at the CPU, I saw it was reporting as an 800 MHz Intel Core i5-7300HQ! Okay, that's not right!
It turns out that Dell hard-coded the firmware to throttle the CPU when a lower-than-expected wattage power brick was used. Even in configurations where that wasn't necessary or made sense. This is silly. I would have much rather had my battery start discharging if the power became an issue, than to silently throttle the CPU. (It's very common to monitor the battery! Not the CPU frequency!) (And no, the firmware warning message that I disabled didn't say that it would underclock the CPU if a lower-spec power brick was used. Just that it might lead to system instability or discharging the battery, or something to that effect.)
Anyway, there is a command you can run in Linux to force the CPU back to full speed. Once I did that, I never had any problems afterward.