1. " cpu fan seemed hard to turn. "
That's not good and could cause a voltage drop that might be what it is reporting.

2. Since we are reaching the end of what I can do on a forum, try this.
Change NUMBER_OF_PROCESSORS: 8 to 4. Here's how and what I do when a PC must squeak by until it's fixed (fan, power supply, board changes?)
Read https://www.google.com/search?q=windows+10+change+number+of+processors

3. 4 sticks of RAM.
Since we are dealing with an elder PC I sometimes move back to 2 sticks to help timing and load on the CPU data buss. If I was there I might change the BIOS to slower memory timing but I'm not so we go with a hardware change.

The SPECCY looks fine unless I missed a thing but the voltage drops are often due to aging of either the PSU or the motherboard. PSUs are commonly replaced with a nice single rail unit of 50 to 100 Watts more than what came out and motherboards next as the same parts that cause PSU degradation are used on motherboards (electrolytic capacitors.)

Electrolytic capacitors and aging is a well worn subject but basically the news isn't good. That is, heat accelerates aging and even in cool machines you see wear that at 4 years you are looking at new boards. Better boards over designed this area for longer life spans but market pressures mean better than hald the designs are 5 year life spans.

Anyhow, try the case cover off for now along with checks on fans, replace bad fans before we dive deeper.