Power Issue?

This is a continuation of this thread.
https://forums.majorgeeks.com/threads/processor-sound-issue.321969/

My computer started running slow after I had it unplugged for an evening. The battery is also not charging, currently just below 74%. After looking around a little more at task manager, my CPU appears to be limited to a top of 13% utilization, or 0.35 GHZ versus a default of 2.80. I've also installed Battery Bar Pro at the recommendation of another user (after virus scanning it), and it suggestests my battery has 25% wear, though I don't know if that is related to my primary issue (the processor; I am, well, less concerned about my battery strength unless I were to return to college at some point I guess).

Reading I've done on the internet suggests that a limitation of the CPU speed is related to power, but this could be the cord, the power supply, or less likely I assume the power in my room itself. Is there a way I could determine this before putting out money?

I don't know though if checking another plug in the house or elsewhere would automatically be registered and corrected by the PC. Oddly enough, the PC itself seems to speed up after awhile, though I haven't yet observed it do so on task manager, since I only just figured that out.

 

Should I buy a Multimeter?

 

I tried restarting in diagnostic mode to disable services just in case that was the issue, at suggestion of website. I also tried updating battery drivers but it did not find any new drivers.

 

There does appear to be an issue with my cable itself, so I've ordered a new one, it should be here on June 24th