On my desktop the power button got finicky. A bit of contact spray around the edges of the button seemed to help. The contacts can oxidize over time. Not sure if this helps all power button problems, though.

It's been awhile since you posted but I'll answer in case you happen to have those old ones around somewhere.
I wish you were my neighbor. If you were determined to throw out a bow over power button issues I'd likely be digging through your trash all the time, LOL
You need to know why the power button doesn't seem to work. It may actually be working and you have another issue or if it's not working it may be an easy fix.

You don't say whether those are desktops or laptops but it seems unusual to have the same issue. Is it possible foreign substances have contaminated the switch? (food, drink, debris from construction, etc)
This can be a problem and although I say "unusual" it depends on individual circumstances. For instance with laptops most people tend to think of them being used as if they were in an office or home environment, however there are people that need them in their jobs that normally work daily in construction or appliance repair, etc... basically environments where there's a lot of debris floating around giving the potential for a bit of "whatever" to get underneath a key.
With laptops sometimes in that case you can remove a key but others you'll ruin the keyboard module so you need to look at the manual to know whether or not you should try to pull a key. Just about every brand has manuals you can download from their site and it's a good idea to get them as it can be harder to find them as time goes by when the OEM wants that space for newer models.

But with laptops you can always use canned air to try to blow out debris and it's good practice to blow out dust from your keyboard just to keep it clean. I say to use canned air because that's what most people will find convenient, I use a giant air compressor that runs 175 psi. That might sound like overkill but all it really means is I have an unlimited supply so I don't worry about 5 bucks a can air, LOL If you happen to have an air compressor the main thing is to make sure there's no moisture collected in the hose as I'm sure you know occurs.
To blow out any keyboard, desktop or laptop is simple and you probably have already thought about just pointing the nozzle at the cracks between the keys... but to do it the best make sure to hold the keyboard (or laptop) in different positions or you may not get all the dust out. It might sound silly but that means if your doing this with an expensive laptop you might need help unless you're comfortable holding it upside down with one hand. You can get by setting it on it edge on each side and such for most cases.
BTW, you can even rinse some keyboards on DESKTOPS under a faucet (disconnected, of course) shake most of the water out and set it aside awhile. BUT don't use a blow dryer, the plastic will deform and the keys will stick. If you have a blow dryer with a "no heat" setting as many do then you're OK, but don't forget or you'll be sorry..

Never use any liquid on a laptop, obviously.

Power buttons on a desktop are replaceable. With laptops they are as well but instead of an individual switch you may be limited to the keyboard assembly, it depends on the particular one you have.

With desktops you're lucky, in most cases you can just put any old generic switch on it. Usually those will be the type that is only "on" when you're pressing the switch (normally open), that means in a pinch you can actually have no switch and "jumper" the ends of the bare wires ...briefly touch them when you'd normally press the button.
Usually you only do a brief press for on or off however when your system doesn't respond you hold the switch down for a few seconds until it turns off. You can jumper it at the connection on the system board as well.

However sometimes they're made so you need to get the switch from the OEM, so a generic switch won't work but they're still not very expensive and it's a fairly easy fix for most people that dabble in light repairs. I have a couple of old Dell desktops that only will work with the OEM switch and I actually disassembled one and repaired it.... most people would have just got a new switch but that's just the way I am, the switch isn't meant to be repairable, LOL.

With desktops there's another thing (couple of things) to be aware of and check that are easily overlooked. One thing is with normally open switches it's possible to have a situation where it's stuck "always closed" , meaning it's as if you're holding the button down all the time. it's something to check if your PC will not come on. If you aren't comfortable taking this kind of thing apart then you're limited to the canned air procedure otherwise you can either check the switch with an ohm meter for continuity or disconnect it to try another switch, or jumper it as described above.

The other thing with desktops is many have a separate "reset" button. (not as common now as in the past). Some are "normally open" like the power switch however some are "normally closed" and it's important to know the difference, but in either case you can just rip it right out by the roots and toss it if you're inclined. You just need to know what type you have so you know what to do without the switch.
"Normally open" means there's no connection unless you're pressing the button, "normally closed" means there's a connection always UNLESS you're pressing the button. Reset switches aren't usually on newer form factor boards but there are some that have them and many of those the connectors are actually there on the system board but they aren't used.

These days a reset switch is something to screw up your OS unless it's an embedded system (like a set top box, for example) or unless you're running Win 3.1. That function is still available to you by pressing the power button down until your PC shuts down, you don't want to do that unless it just won't shut down at all because it usually means some sub program is still working. Give it a few minutes and it may shut down, if not push the button again and give it some more time. It's not usual for it to take more than a few minutes to shut down but it can happen even on a normally functioning system under some circumstances... if you push your PC to the limit processing video or something "memory intensive" You may be into the swap file because you don't have enough RAM for instance... in which case if you need to shut down your system you'll lose that work if you force it.