Firstly, the Dell Optiplex 990 is an older machine, which I was aware of. Before purchasing, be aware that you need a Windows product key, otherwise it won't boot. You need a disk or you can easily download Windows from another computer into a USB. And as for a product key, there are decent people in this world that post their product keys online. 100% legit, no problem.My intention for this purchase was to see if I could I build an inexpensive retro game emulator PC. So I kept the additional components on the cheap side. I wasn't expecting much from a $130 dollar machine, so I knew it wasn't going to be too fast. The first thing I replaced was the hard drive with a used Samsung 860 EVO SSD on eBay  for $75 bucks. You can boot your machine from the SSD, at a significant rate. In my case the HDD booted my machine in 4 and a half minutes. The SSD was in under a minute. Loading programs is never a problem. Now it's a $205 machine.The next thing I needed to game with was a Graphics card. I bought a MSI Gaming GeForce 710 2GB GPU on eBay for $35. What that did was give me an HDMI port and upgraded the resolution on my machine once I downloaded the drivers. Up to 4k. But I brought it down to 1440p. I wasn't able to get any audio from my VGA cable at first, but once I downloaded the NVIDIA drivers, I was able to get audio to my TV, via HDMI. My machine was now $240. I did NOT have to upgrade my power supply or anything.I wasn't expecting a free mouse and keyboard from the seller, which is appreciated. I took that to work since I didn't need it. I bought a cheap Logitech wireless keyboard/touchpad combo for $15.I love my $240 setup since I was able to successfully build onto it. I watched endless YouTube videos on installing these components and it is not as intimidating as it looks.