I'm in the process of getting my Home Assistant environment up and running, and decided to run a test: it turns out that my gaming PC (custom 5800X3D/7900XTX build) uses more power just sitting idle, than both of my storage freezers combined.
Background: In addition to some other things, I bought two "Eightree" brand Zigbee-compatible plugs to see how they fare. One is monitoring the power usage of both freezers on a power strip (don't worry, it's a heavy duty strip meant for this), and the other is measuring the usage of my entire desktop setup (including monitors and the HA server itself, a Lenovo M710q).
After monitoring these for a couple days, I decided that I will shut off my PC unless I'm actively using it. It's not a server, but it does have WOL capability, so if I absolutely need to get into it remotely, it won't be an issue.
Pretty fascinating stuff, and now my wife is completely on board as well; she wants to put a plug on her iMac to see what it draws, as she uses it to hold her cross-stitch files and other things.
7 months later update:
I've expanded HA quite a bit and have a decent grasp on where my electricity is being used. Suspending my desktop has saved a shitload of power: under Linux, when suspended, it draws ~10W of power at any given time vs ~100W when idle. Also, I put smart plugs on the server cluster; the total usage of the entire cluster - 4 mini PCs, 1 SFF, and 5x HDDs (NAS) - over the last 7 months so far is currently at a whopping 465 kWh. That's ~66 kWh a month. Barely 5% of my monthly electrical usage.
How is it possible that it draws 100W at idle? What is it even doing?
Hard drives, especially spinning discs, and RAM are probably the biggest factor at idle. I dropped my servers' idle draw from 220w to 180w by dropping it's RAM and replacing some older drives.
People underestimate how more RAM can be more power usage.
The PC was drawing ~90W. All solid state, no spinning rust. Lots of fans though, since it's air-cooled. Not entirely sure what was causing the draw, but it's definitely something I want to investigate at some point.
Check your GPU power usage, I remember seeing people complaining about theirs not clocking down if they had a second monitor plugged in, and similar bugs
Worth a look. One monitor uses HDMI, the other uses DisplayPort. They're just cheap secondhand 1080p monitors to get me by until I toss them for an ultrawide 1440p unit.