You remind me of a friend of mine that seems to find ways against the odds to bugger things up 😀
Having said that I recently put the Dreamblaster S1 in backwards in a sound card and fortunately all it did was stop
the computer from turning on. I wasn't being careful and didn't properly look into what I was doing first, which is
way less acceptable for me as I'm and electronics tech.

I would strongly suggest in future posting here before attempting things like this, and post photos wherever possibole.

As far as Your motherboard and cache is concerned, carefully remove all of them and see if the motherboard still boots. Putting one in backwards will
most likely kill the chip. I would think they need to be matched probably, consult the manual if You have one.

I did that mistake too with my IBM PC340 (pentium 100 cheap IBM)
The cache chip surely died, but the computer still works (I never managed to have working cache in it though, it was just one morr failed attempt that ended horribly for the cache chip)

The chip is dead as hell. It sparked visibly and has a giant hole in it.
The board boots, but I have no more 4 stacks of chips to test and this board never did like 64k or 256- just 128. Seems to be common with the boards I've gotten.
Oh well, put it aside and buy some from Ukraine.

What motherboard is it? model number and/or photo helps.

You can often get cache chips new off Aliexpress and some Ebay sellers.

I learned that you /can/ mix and match and was able to cobble together something working.
I also found out that the majority of other chips I had are bad which explains my problems with the other boards, they all just take to bad chips differently. One will boot and then crash soon.

Doesn't explain why they worked with an SX but not a DX2, but I found that out too just now- they work fine, all of them, at 25FSB. 33 kills around half of them.

How many nanoseconds are they made for ? (I'm probably saying this sentence the wrong way ... sorry for the bad syntax, english isn't my native language)

25, one of them- I believe it's a TAG, is rated for 20 but absolutely doesn't work.
I think the problem is I have bad tag rams, and this board- the one I exploded- doesn't require one. The other fancier ones do.