SSD Samsung being the boot drive - correct? Down to 16% free space. I keep my drives in the 30-20% free space range. That is just me and there are other views about the range. Just let the free space as is for the time being.
Hopefully PSU is okay. However, there are many factors involved so it is a bit to early on in the trouble shooting process to rule out the PSU.
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Power down, unplug, open the case. (If you are not comfortable doing so on your own then find a knowledgeable family member or friend to help.)
Clean out dust and debris,
Verify by sight and feel that all connectors, cards, RAM, and jumpers are fully and firmly in place.
Copy down PSU make, model, efficiency (bronze, silver, gold, etc...) Post accordingly.
Inspect for signs of damage: bare conductor showing, melted insulation, kinked or pinched wires, browning or blackening, swollen components.
Then work and game as normal.
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If the stutters continue then open either Resource Monitor or Task Manager to view system performance. Use both tools but only one tool at a time.
View performance: 1) after boot up while the system is just idling, then 2) view while doing light work or browsing, and lastly 3) while gaming. You will need to keep the tool window open to watch what is happening to system resources especially when you notice the stuttering.
It will take some trial and error to figure out how each tool works and what it shows. Take your time. Note that some column headers contain a small upward or downward pointing arrow. Clicking the arrow changes the sort order. Helpful if things are "jumping around" too fast to watch.