Is it possible to monitor the current being drawn by a computer from an outlet using built-in tools like a terminal? I know some systems can report power usage, but if I dynamically reduce the current to a level below the maximum the computer can handle, would I be able to see that current value reported somewhere in the laptop?
If this functionality isn’t built into the system, is there a way I could implement it myself?
Not without adding hardware.
the TP link kp115 can monitor a single outlet.
The hs300 is an outlet strip with 6 outlets individually monitored.
A python script exist to collect power consumption stats for TP link kasa devices.
These can be monitored from the app on a phone or you could setup external monitoring like homeassistant OS.
A very small number of computer power supplies do offer this feature. I have a corsair power supply that reports how much power it uses. Only a few models they make even support this option.
Here is the one I have. This is a power supply for a desktop PC.
Here it is graphed in homeassistant via kasa hs300
There is no way to tell this accurately without additional hardware as there are no connections from the PSU which send that data (and indeed I doubt its being monitored in the PSU). You may be able to estimate it based on state of charge of the battery and consumption but it will likely be crude.
There must be multiple ways to externally monitor power draw using a device on the input to the PSU. One way would be to use an ESP8266/ESP32 based power controller that includes power draw monitoring. I've had good success using Shelly 1pm devices (https://www.shelly.com/en/products/shop/shelly-plus-1-pm) which can be easily read using http requests and/or MQTT. I have no doubt there are other cheaper brands which do exactly the same thing or can be made to do so using Tasmota - but I use Shelly's because they are easy and permitted in my country. Welcome to the world of IOT devices.
Note there is almost certainly a level of disconnect between your usage and what the battery is doing - so depending on your use case (ie the why) and your hardware this may be an XY problem. Its noteworthy that USB-C and even many older laptops have a negotiation of maximum charge rate between the laptop and charger - maybe you can take advantage of this and use a lower amp charger that negotiates max charge rate?
There is a device called a "kill a watt", it is useful for getting a good grasp of electricity draw in any 110 outlets.
