I've only just noticed that my Windows 10 PC is using the Samsung High Performance power plan. This must have been set up when I installed a Samsung SSD a year ago, along with the Samsung Magician software. For most people, a small tweak to this plan will reduce energy usage without decreasing performance.Looking at the advanced settings in the power plan I spotted that the Minimum processor state, under Processor power management, was set to 100%. This means that the processor runs continually at its maximum frequency, regardless of load.
Changing this to a lower number, such as 5%, allows the CPU to lower its speed when it is not doing intensive work. When it was introduced, dynamic frequency scaling was a major marketing feature, as the system will run cooler and consume less power, with no decrease in performance. In Windows 10 current frequency can be seen in the task manager, labelled as Speed, and can be compared with the highest possible frequency, labelled as Maximum speed. In the screenshot below my system is running at 1.22 gigahertz, and could go up to 2.90 gigahertz.
After this tweak to the power options my system has been quieter, as the CPU fan is able to run slower, and has been using less energy. I'll remember to keep my eye on this setting in future, as who knows what other software might make its own adjustments to my carefully configured power plan.
Intel's version of this option is called SpeedStep, and AMD's is Cool'n'Quiet. You can read a lot more about minimum processor state in an answer at superuser.com.