That 4.5 year old EVGA PSU is a likely suspect.
Works but not longer can fully respond to flucuating and peaking power demands.
Take a look at the following link. Not with the immediate intent to go out a purchase a new PSU. Simply to apply the various calculators and total up the system component's power demands. If a component has a wattage range then use the high end value.
I also believe that the drives are also involved. Space being limited and more time (power) is required to read and write data. Especially the HDD.
Once fillled beyond 70-80% capacity then files may become fragmented and problematic. HDD's can be defragmented. SSD's cannot.
Backup all important data to other locations then do some slow and care disk cleaning to removing unused apps, old data, and (likely) many temp files.
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Power down, unplug, open the case.
Clean out dust and debris.
Verify by sight and feel that all connectors, cards, RAM, jumpers, and case connections are fully and firmly in place.
Check for any signs of damage: bare conductor showing, melting insulation, pinched or kinked wires, browned or blackened areas, loose or missing screws.
Just a bit of maintenance and care could help. Cleaning out dust, for example, will allow the system to run cooler.