Honestly, choosing a PC to optimise idle power consumption is not something that can be addressed in a single buying advice thread, the subject is very complicated and you have to pull information from many different sources to make an informed decision.
My personal opinion would be that the difference between an optimised and unoptimised build (often around 30 to 50 watts, which might cost you £50 per year or so, if the PC is idle a lot) is unlikely to trouble someone buying a high-end PC.
If you're still interested in doing this, then I'll try to answer your question without writing a novel.
To optimise idle power you have to care about
everything. This is because the lower your power usage goes, the more difference everything makes. What I mean by that: if you have a CPU and graphics card that uses 500 watts combined, then with a motherboard that uses 10 watts more on average, who cares? However, if that motherboard adds 10 watts to idle power, the difference is
way more meaningful and it matters much more.
Generally speaking, the idle power figures in 'normal' reviews are nearly useless and the main reason why (at least, in my opinion) is because reviewers just include it as a courtesy or a curiosity, they're not really interested. That leads to very unreliable test conditions and even if they do care (which most don't), they're often using review samples and very early hardware, which is rarely optimised properly and early firmware/drivers can have a big impact on the review numbers.
To give you a ballpark, the difference between an optimised and unoptimised choice of CPU, motherboard and graphics card can be anywhere between 5 and 30 watts, each, with the average somewhere around 10.
Some general rules:
- Contrary to what you might expect, bigger/higher-end CPUs rarely use more (or not much more) than smaller/lower-end CPUs.
- If you have a very bursty workload, then it can be worth turning off, or scaling down the turbo, to avoid unreasonable power usage when just browsing, but this can have a big impact on long-run workloads if it isn't done right.
- Bigger motherboards and higher-end chipset use more power (at idle) than small boards, with low-end chipset. ITX motherboards are usually the best option, regardless of brand and price.
- RAM and SSDs are rarely worth considering, but as FredFlint mentioned, your RAM speed can have an impact on the CPU (I believe this issue also existed for AM4 CPUs, where they used more power at idle when the RAM was above 2666/1.2v).
- HDDs ARE worth considering, since some (especially older HDDs) can make a big difference.
- High-end graphics cards can use a lot more power at idle than entry-level ones. In some cases they can use more power than the rest of the system combined.
- Graphics card idle power is (strongly) influenced by how many monitors you have and what refresh rate they're running at, though driver updates and tweaking can address this.
- Case fans don't have a big impact, unless the idle is really low.
- PSU price, efficiency rating and quality tend to be meaningless to idle on the average desktop PC, i.e. a crappy budget PSU may be more efficient at super low loads than a £200 Titanium rated PSU. The best PSUs are actually mini/Pico (or 12VO, which is what OEMs use) rather than ATX, but these are unlikely to be suitable for a high-end DIY PC.
- BIOS and driver optimisation can make a big difference in some cases (e.g. 10 watts).
- Certain devices, or poorly written/unoptimised software and drivers can prevent the CPU from idling properly, for example: Ryzen had an issue with Discord and Steam (not sure if this still applies).
The best sources for idle power:
- NAS and server forums.
- User posts which include ALL their specs.
- Threads on large forums which are specifically dedicated to idle power and/or efficiency, e.g.
here.
YouTube videos that focus on power efficiency and undervolting can be helpful too.
