If you like to tinker with computers, then you probably often run across a scenario where you're testing hardware outside of a case. If it's ATX, then you need a way to power it on since the case has the soft power switch. You can locate the front panel header and use a flat head screwdriver to short the two pins for the power switch.
I always use to just use a small flat head to short the pins, and I still don't mind doing that if it's just a quick one and done test for something. But I wanted something safer for the times when I'm tinkering with something continuously. Years ago I would throw caution to the wind, but now that vintage PC hardware can be expensive I'm concerned with slipping and accidentally shorting something out. And I also wanted something more convenient too.
I know you can purchase these ready made, and you can get them especially cheap from China. But you may have most if not all of the parts already lying around to make your own. And when you make it yourself, you get to make it the way you want. Like wire length, for example. Or the switch size, shape and color. I already had everything I needed except for the switches. Since I was ordering from DigiKey anyway, I also grabbed a couple of switches (otherwise shipping ends up costing more than the parts, which is always frustrating).
Power switch: https://www.digikey.com/en/products/det ... gExAF0BfIA
Reset switch: https://www.digikey.com/en/products/det ... gExAF0BfIA
Nothing special, I just went with price and availability. I wanted a switch that looked like it would be easy to grip and push with one hand. This square switch seemed like it would be easy to one-hand with the mounting flange that it has. I got one red and one black, so if I have both plugged in at the same time I can differentiate between them.
If you want to make your own, you can get cheap switches from eBay or whatever auction site. You just want a momentary switch that is normally open (NO). So look for SPST-NO (single pole single throw, normally on) that is Off-Mom (off, momentary). You actually could use a latching switch if you have some lying around, but you'd have the annoyance of having to turn them back off every time you use it.
Now you just need some female Dupont connectors. With bread boarding, Arduino and similar, they are cheap and plentiful on eBay and the like. Just search for "Dupont wire" and you'll get a ton of results. You will find both male and female connectors, just make sure at least one end of the cable has female connectors (what you need to connect to the male pins on the motherboard).
If you have wire with Dupont connectors on both ends, just cut one end off and then solder the wires to your switch. Doesn't matter which wire is which since you're shorting them together anyway. You should insulate the pins for safety.
I wanted it to feel a little firmer and look a little neater, so I ended up slipping on another larger heat shrink tubing around both wires.
And that's all there is to it!
Using the same method, you could easily make a power on light using an LED. This can be very useful if your CPU has no fan, the motherboard has no LEDs, and the PSU you're using is a modern one that is dead silent. It can be hard sometimes to determine if the board actually powered on.