My AMD FX-9370 died. A good five years, half as a desktop, half as an ESXi server. Back then, 32 GB was the max for a free ESXi license, which was all my Asus Sabertooth 990FX motherboard could handle anyway. Never did max it out, but could of, would of, should of. All of this was inside a Thermaltake Overseer RX-1 which made it a BEAST! It was my first time doing a custom build since my high school days. I have since build many more.
My kids relied on this ESXi server because it housed their Minecraft server, which only eats two cores and some mediocre memory (more since there are 4 Minecraft servers running at the same time), but those two cores take a beating with a lot of chickens. º_o Had to get a decent build for it.
So when I rebuilt, I mainly focused on the CPU and the budget, though I also have been keeping my builds small, as well.
With ESXi mainly being headless, I went with the i5-9400F which doesn't have integrated graphics. This barely kept me within my budget at the time while keeping the CPU benchmarks high for a single thread. If I had to do it over, I'd have gone with the i5-9400 so I could use the integrated graphics when troubleshooting instead of throwing a GPU card in.
I then proceeded from there to size up a motherboard. Lately, I have been quite impressed with ASRock. They are great high performance, yet lower priced without compromises. I have two PCs with their motherboards and built or helped build others and all are great. I almost always try to get Mini-ITX to keep it small. I considered Micro-ATX, but wanted to keep options open for going with a 1U rack mount case rather than a 2U (though I finally compromised and went with 2U).
Memory for me isn't that big of an issue. With ESXi and mainly being for server purposes, I didn't need much. I went with the Crucial Ballistics DDR4-3000 because it was fast and cheap. No OCing. I like to keep it stock anyway so it runs longer and stable. ESXi will allow unlimited memory, but being Mini-ITX, I am limited to 32 GB anyway. For my purposes, that is good enough. I currently have one stick of 16 GB and will upgrade to 32 GB if and when it is needed.
I just grabbed an old 1TB HDD. It was from an external that I gutted when the controller failed. The drive itself was in excellent condition (1 month powered on time) and benchmarked very well.
The Corsair CXM 750W is overkill by FAR! However, that is what I had on hand. Been a good PSU.
The case is a PLINKUSA 2U Rackmount Chassis 14.17" Deep Micro-ATX/Mini ITX (IPC-2360F). It has it's pros and cons, drastically in both directions. Again, this was a server build and I struggled the most with which case to get. I will explain later other alternatives I considered, but for now, I will explain more here since this is my main reason for even diving into explaining my build. There are not many builds that explain and help understand the rack mount case solutions out there.
There are a few main brands out there I considered. PLINKUSA had a lot of good options, but so did iStarUSA and Rosewill. SuperMicro is an honorable mention, though I didn't give it much thought (a little more expensive). In my application, I have an old network rack enclosure that is 15" deep that work no longer needed and I intended on using. I tried to keep it within 14" and this case was 14.17" according to the specs. I measured it when I got it and it was actually 14.25" and I really underestimated how much room the power cord uses. Next time I will leave 2" it. Even with a right angle, 1" is a minimum and this won't work for my network rack enclosure. I bought a free standing 12U desk rack (RK12OD) anyway for $45 made by Startech.com. It is a little wobbly, but it works. It uses the square nuts which was a HUGE plus. A lot of reviews say it didn't come with enough nuts and screws, but compared to what you get out there, I cannot complain.
The PLINKUSA IPC-2360F has USB 3.0 ports, which is more than most other rack mount cases can say. It doesn't spell out clearly, but it does indeed come with 2 fans. I wasn't expecting that. They move a lot of air, but they are NOT silent. Being 2U, it has room vertically for a standard ATX PSU. HOWEVER, there is no ventilation for it, above or below! That is a big oversight on their part. The power light is REALLY bright. I have it sitting on my desk and at night, it lights up the room. No big deal unless I have a guest sleeping on the couch. The hard drive mount and PSU are dangerously close. I could see issues arising with power cables and data cables fighting for real estate easily (see pictures). Also, I found a chip in the paint less than 20 minutes after unboxing it. Not sure if it was from dry fitting it in the network enclosure or it came that way. Something to consider if you are about appearances.
Anyway, I hemmed and hawed over the possibility of the iStarUSA D Value D-118V2-ITX 1U Rackmount Mini-ITX Server Chassis. This would have required a Flex ATX 1U PSU rather than the standard ATX. But considering the case is super cheap, I was willing to go that route. It would have been a lot smaller at 11" deep and only 1U!! I might actually do this later anyway and rack mount my "desktop later." If I would have done the 1U case, I would have gone with the Seasonic 250SU 250W 80Plus 1U Server PSU. It's reviews indicated it was quieter and more reliable than the Solid Gear SDGR-FLEX320 320W Mini-ITX / FLEX ATX PSU I considered. More expensive, but a good compromise. I would have also had to switch from the stock Intel heatsink\fan to a 1U fan like one from Dynatron (K199) or Silverstone (NT07-115X).
Because of the size requirements I had, most of the other cases I considered were all PLINKUSA ones.