This is a tough one. CF is essentially IDE, just in a smaller pin pitch package, which consequently makes CF to IDE adapaters exactly that -- adapters. No electronics or protocol translation needed, and the only circuitry at all is usually just a voltage regulator and maybe a couple filter capacitors. This means that the adapters are pretty simple, and equally hard to screw up... even the cheap ones.

The two things I can think of are that the CF card and adapter do not match in voltage (i.e. adapter is configured to supply 3.3V but the card is 5V or vice versa), or the card itself is bad. Are you able to try a different card? The adapter you linked to looks to have a selectable voltage, so ensure it matches whats written on the card.

I've tried both voltages and have gotten the same results with both. Also, I've tried it with both the cards I use with the working two CF adapter with the same results with both (one has Windows 95 on it and one should be an empty FAT drive).

The Ebay page for the one that works is no longer available. This is written on the adapter itself however:

CF-IDE40 Adapter v.A1
DMA mode/vcc from IDE pin20

In case this offers anything useful.

Are you using new CF cards?

If so, boot with your MS-DOS floppy, and run

fdisk /mbr

I have to do this with every factory new CF or SD card.

They aren't new CF cards, and I can't even boot into DOS as it will hang just after "starting MS-DOS" when I try, at least with the MS-DOS install disk (I can't find my startup disk for some reason).

EDIT: I just want to clarify that the cards still work perfectly with the other adapter, and the boot disk works just fine when the CF card isn't in the new adapter.

It looks like the one I bought is a knockoff of this:
https://www.amazon.com/gp/product/B001JTO782/ … 1?ie=UTF8&psc=1
Package looks exactly the same and everything, except for having no brand name instead of Syba. I have a hard time believing I got 3 faulty adapters in a row, especially since ebay says over 100 people bought the latest one I got, but I suppose this could just be a case of cheap knock-offs? Still, the one that works was a cheap one from China so I'm completely at a loss. I would get the other ones that didn't work to test with, but I can't remember where I put them at the moment.

Maybe a stupid question, but is your boot order set to boot first from floppy and then from harddisk ?
I had a similar problem (the card wouldn't boot, but worked when booted from floppy), but the fdisk /mbr trick fixed it.
I'm using an internal CF to IDE adapter so that won't help you ( https://www.aliexpress.com/item/T-CF-to-IDE-C … 2319799882.html ).

It's really strange. All of my retro PCs have a CF adapter for easy data transfer, and except the two 3.5" front panel adapters, all of them are back panel models, 2-3 USD (shipping included) items (i.e. very very cheap). All of them are working well, so yes I believe 3 broken adapters in a row is very unlikely.

Just to be sure, did you check the same system, which is not working with your adapter, is actually working with other IDE devices like HDDs?

Is this a system that is properly working with your former other adapters that you mentioned as working?

Is your BIOS parameters are ok? Can your BIOS support the CF card you are using, if it is larger than 512MB/2GB/8GB etc.? Can your BIOS detects the card during preboot?

Another stupid question... how are the power jumpers set?

In my CF-IDE adapter there is a power connector (like those on 3.5 inch floppies), a jumper that selects the power input and another jumper to select if your card use +5v or +3.3v.

The power input can be the pin 20 from IDE connector or the power connector, and I guess that if you select the wrong input (i.e.: power from IDE connector but your board does not send power through it) it won't work. Try to select external power input and connect it to your PSU to be on the safe side.

The other jumper usually doesn't matter because most CF cards are capable to work on both +5 and +3.3v (but remember that you can find a card that needs a specific power supply).

Also, there are some mods to get that power supply from IDE on devices/boards that doesn't send power on pin 20 (i.e.: the divide interface for ZX Spectrum), but on a PC your best bet would be using the PSU.

Ok,I'm using the same system with both the working adapter and the not-working one. I haven't tried the system with a normal IDE drive, but it does work just fine with an IDE CD drive. BIOS does see the drive even with the not-working adapter. I have BIOS set up to automatically get the drive specs, but I didn't see if all the detected specs are the same between the non-working adapter and the working one. I suppose it's possible it's getting the wrong information?

I use a floppy power connector, and with the power source jumper in both locations. As I recall, both with the floppy connector unplugged and with the jumper in the other location, the lights on the adapter would turn on but wouldn't be quite as bright, and BIOS would hang for a while when trying to get the drive's specs, and wouldn't see it. I've also tried the voltage jumper in both locations with no difference.

This sounds like a DMA problem. Using a DMA enabled CF card in a non DMA enabled adapter will cause boot problems.
Some of the cheaper Chinese adapters don't support or implement DMA correctly on the adapters(or jumpers have to be set correctly).
If you have both DMA and older non-DMA CF cards try both in the adapter to rule it out.

@AvalonH That really could be the issue here. Some adapters aren't fully wired, either.
A non-DMA capable adapter looks like this, for example.:

It's not a bad piece, though. Build quality is decent, and so is the soldering.
For a 286 or so, this one is just fine, I think. For modern 3.3v-only cards (if they actually exist),
someone could also make an additional power cable with two silicon diodes in series (resulting in ca. 3.5v).

Here's one adapter which I had good experience with. It's similar to the one ocdmonkey mentioned.
It supports all kind of feature's and is ideal for modern CF cards and Windows 9x.:

This one officially supports DMA (and Ultra DMA cards), master/slave configuration, 40pin and 44pin IDE cables,
power via IDE, 5v and 3.3v (has its own voltage regulator). It also includes a rear bracket and has LEDs for read/wite activity, etc.

Edit: Oh, I forgot something. Some adapters require the CF card to be inserted upside-down!
I initally thought my adapter was broken, until I found out. Haha! ^^
Wait, here's a picture of it:

Ok, I finally figured it out. All the adapters were working just fine when I used them with an IDE to USB adapter. After I tested that I kinda got a eureka moment that my '95 for whatever reason wouldn't work with the card correctly unless there was a slave on the cable. Sure enough, I tested this theory and it worked perfectly. I have no clue why this would be a thing, since it used to have just one traditional HDD in it (though that HDD couldn't be read with my USB adapter =/ ), but I finally got it working about how I want it to.

one thing nobody has mentioned is you need to be using the phoenix implemention of LBA, most mobos switched to it. IF you can get to 'Starting MS-DOS' and it hangs, its loading part of the disk but not others, which points to a geometry problem which to me screams LBA issue.

I just get Non system disk or disk error, no matter what system i use, i tried it on the ASUS P2B, Intel Advanced/ML, ASUS TX97-XV, other boards, no dice 🙁. any suggestions, is my adapter DOA, do i need to RMA? or is my CF card shot, cf card only works fine on my main PC with Windows 10 in the usb card reader

Sounds to me you need to format it correctly so that it's bootable. fdisk /mbr

The issue happens when i transfer games and programs to it from my Windows 10 PC with a USB card reader, it somehow corrupts it and makes it refuse to boot. The reader is a el-cheapo one that i got from walmart, it feels shoddy but it gets the job done

I transfer games to CF in a similar manner, but my transfer CF is not the disk I boot from. Does the disk actually corrupt or does it only become non-bootable?