I read somewhere that the "S" version is the short ATX 24 pin cable. Let me see if I can find the reference.
Here is the comparison on SMC's eStore description of both PDBs.
Could someone help me with figuring out whether 826 PDBs are compatible with 825 cases? I'm completely new to server chassis, and just got a few 825TQ-R740LPB cases the other day, with nothing inside them. If I buy PDB-PT826-8824 - would it fit in the 825TQ-R740LPB cases (so I could then get 23 pair PSUs like PWS-1K28P-SQ, for example, and use them in my cases)? Or do I have to stick with the "officially" compatible PDB-PT825-8824, thus limiting myself to using 19 pair PSUs (like PWS-920P-SQ)? It just seems like the more interesting PSUs are all with 23 pair connectors, but I don't understand whether I could use them in 825-series chassis.
I won't be able to do this since I don't have the old housing(s), the chassis I've got are literally empty, only 3.5" caddies were included and nothing else. Don't even have the power/reset buttons and LEDs for the front. Hopefully PDB-PT826-8824 and PDB-PT825-8824 have identical housings, and I'll just be able to put the 826 PDB into my 825 chassis.
Right now there's basically one listing on ebay for $90 or BO. PT847-8824 are available for <$50 new, seem to be even compatible with my SC825 chassis (at least the seller says so). But then that seller also says that they're for 19 pair PSUs. When I count the number of pins on the pictures, it's 27 though. Damn, all those Supermicro numbers are confusing, can't even find PDB-PT847-8824 on the official website. Figuring out SAS/SATA backplane compatibility is probably gonna be as much fun. 
I don't know, I might be not looking at it right, never saw any PDBs in real life, only pictures on the internet. Here's the original PT825-8824, that obviously fits (but only mates with 19 pair (more expensive) PSUs, which I'm trying to avoid and thus looking for a 23 pair alternative):
which might be naive and wrong, of course, and there might be something I'm not seeing.Yes, PT825-8824 should fit, it is the standard PDB designed for SC825 chassis after all. I'm just trying to build a simple home lab setup as cheaply as possible. For a 4 node cluster, 4* PWS-920P-SQ would cost me $340 shipped, and 4* PWS-1K28P-SQ are $150 shipped. I'd like to get at least one or two spares as well, or maybe even just go with 2 PSUs per chassis, and that turns it into $680 vs $300. Considering how I don't have any PDBs in my chassis yet anyway, it made sense to try getting ones made for 23 pair PSUs, rather than buying the standard PT825-8824. While researching the possibilities, google led me to this thread and your post #5 here caught my attention - I thought I could get away with putting 23-pair PDBs into my chassis. Not sure whether it's even an option though, considering how none of the alternative part-numbers found so far seem to have the matching hole pattern.
