XPS 8950, incomplete implementation of horizontal HD design

I have a DELL XPS 8950 and it has TWO Hard drive metal carriers that accept 3.5" cages/caddies.

Where I get confused is that DELL ran SATA power cables up to each HD carriers with TWO SATA power connectors for each HD. That's a total of (4) SATA Power connectors.

The "EXTRA" SATA Power connector hangs of the original main power cable just 1" short of the end of the cable. See picture.

Am I to assume this an extra power connector for a HD or SSD?

Can I run FOUR  3.5" HDDs in total on this PC ? 

If so, does DELL sell Hard drive metal carriers that accept 3.5" cages/caddies? Because if this "EXTRA" SATA Power connector is for powering an additional HD or SSD I'm going to need the metal carrier in order to mount a HD using a Cage/caddy.

Does Dell sell Hard drive metal carriers that accept 3.5" cages/caddies that attach directly to the existing HD so that you can stack the HDs? Or is this something I can find on Amazon or NewEgg?

Re: Am I to assume this an extra power connector for a HD or SSD?

yes the extra power connector is for a second hdd or ssd but it has to be two 2.5" drive per cage if both power connectors are to be used.  You can use a Dell 2.5 to 3.5 adapter to install two 2.5" drive.

Original Dell Optiplex 2.5"SSD - 3.5" HDD Adapter Bracket Caddy Tray R494D F767D

Dell design is for one 3.5" hdd or two 2.5" hdd/ssd per cage.  since there are two cages, max 4 x 2.5" hdd/ssd or two 3.5" hdd.

But I don't want to use 2.5 SSD drives. I want to use FOUR 3.5" HDs @ 4TB each.

Can the power supply on this unit handle it?

As you already noticed the pair of Dell precut sata power connectors for each HDD cage are too close together to reach dual 3.5" hdd stacked in piggy back fashion.  The HDD cage is not designed to accommodate two 3.5" hdd stacked either, but you can use zip tie or some other way to mount one 3.5" hdd outside HDD cage.  You can use a right angle sata male to female Y split extension cable to get around the Dell precut connector constraint. 

standard 3.5 hdd thickness: 26 mm or 20 mm

standard 2.5 hdd thickness: 9.5 mm or 7 mm

Red nailed the answer on the spot.  The extra power connector in question was custom designed to power dual 2.5" drives.  With proper caddy, you can fit 2 drives in each cage to have x4 of 4 tb SSD.

Dell does not sell the metal cage for upgrade parts and accessories.  Although there are 4 SATA ports on board, installing x4 three and a half inch drives will require some kind of hack/mod to the case.  If you prefer spinning drives, it would be a lot easier to use x2 higher capacity drives instead.

Good luck fitting four 3.5 drives into the 8950 case. If you get creative enough and are decent at fabricating you should be able to accomplish it. Depending on what power supply you have and what GPU you have, the power supply should be able to handle it. That is a lot of storage space. I would personally just get a large external drive for that and put all SSD in the case. I take it you do not have an optical drive or are planning to disconnect it and also use that SATA port on the MB?

can you please illustrat how that would actually hook up?

There is actually room to fit 2 extra cages for 3.5" in this case. One on top and one on bottom.

My PSU is 460 watts.

I find it strange that Dell can't provide me the metal cages to insert my 3.5" sata drives into. 

I also find it strange that your answer is to just spend more money and convert everything to expensive flash SSD dives. SSD drives for just 2TB are 2X+ expensive vs. HDD. You are discounting the obvious problem when people upgrade their PCs is that they need a place to house their 3.5" drives from their old PCs.

Is there a specific reason that you need 4 HDD's? There are lots of good reasons to be irritated with Dell but not being able to put four 3.5 inch drives in a PC that clearly says in the specs that it has two 3.5 inch drive bays isn't one of them. If you don't want to spend the money for SSD drives maybe just get a couple of bigger HDD's or an external one. If it is that important to you to have four 3.5 inch drives, I suggest you talk to Dell about returning the PC and doing a custom build.

This video shows how to remove the Dell top left hdd cage (5:00).  It also shows there is a raised shelf on the right side of cage which would prevent user from installing a third 3.5“ cage between the top left and top right cages.  In order to install a 3.5” cage in that space, one needs first to mod the top left cage by removing the raised shelf (beware that would void warranty and the shelf is designed for some potential purpose) .  After that step there is still no mounting mechanism provided in chassis to fasten a third cage up there.  Further mod of chassis is needed.

To make it easier, one could piggy back two 3.5 hdd cages on the lower right corner of chassis.  One could use the Dell XPS 8920 8930 3.5" Hard Drive Caddy w/Cage 4W2CH 65KHD which are stackable. To power the #3-4 hdd, 1-2 long sata power extension cables with right angle connector are needed too.

https://www.ebay.com/itm/Dell-XPS-8910-8920-8930-3-5-Hard-Drive-HDD-Caddy-Bracket-13P1-4ZN0301-5YM97/352355211538?

https://www.ebay.com/itm/Lot-of-2-Dell-XPS-8910-8920-8930-3-5-Hard-Drive-Cage-Enclosure-13P1-4ZN0301/155132232961?

YES!!!!!!! this is what I need. Where do I buy it?