Laptops that supports second internal hard drive ?

SOME current Dell systems support dual hard drives (some support even more), but definitely not all of them.  And even among the systems that support dual drives, the connectors are different.  As you've noticed, some can have drives installed into their optical media bays, others have a mixture of SATA and mSATA/M.2 connectors, and still others just have multiple M.2 connectors.  Some laptops that have a WWAN slot (mobile broadband) can accept an mSATA SSD installed there instead if you don't want WWAN, but that's not true of every system with a WWAN slot, and information about which models can accept mSATA in their WWAN slot unfortunately isn't readily available.

One way you can get a pretty good idea of whether a current system supports multiple drives is to look at the configuration options available from the factory.  Obviously if the factory offers it, then it's possible.  If the factory does NOT offer it, then it MAY still be possible, but that would require more research.  Unfortunately I don't know of a list specifically for which current Dell models support more than one hard drive.

In addition to the above, if you specifically want a 2.5" spinning hard drive rather than dual SSDs, that narrows down your options quite a bit because those drives are quite large and bulky compared to M.2 SSDs these days, so they're being eliminated from smaller laptops.  I don't think you'll find any Latitude or Precision models with displays smaller than 15" that will accommodate a 2.5" SATA drive.  I know the Precision 5520 (and its sister system the XPS 15) both support 2.5" SATA drives as well as an M.2 SSD as long as you order the smaller battery, since the larger battery fills the space that the 2.5" drive would use.  The Precision 7000 Series models also support two hard drives, and I think at least the 17" model supports 3 or even 4?  I can't remember offhand, and you can find out yourself by checking the configuration options anyway.

On the Latitude side, the 5580 and newer 5590 offer configurations with a 2.5" drive as well as M.2 SSDs, so chances are very good that they can both be installed at the same time even if that isn't offered by the factory, but again you may have to get a smaller battery.  And if you go this route, I would also suggest ordering the system with the spinning drive from the factory and adding the M.2 SSD yourself, because on some systems Dell requires a caddy and ribbon cable to connect 2.5" drives to the motherboard, and if the system wasn't ordered from the factory with a 2.5" drive, those parts aren't always included.  You can usually buy them from Dell Spare Parts, but it's more hassle.  By comparison, installing an M.2 drive just requires you to pop it into the slot (which is built onto the motherboard anyway) and than add an screw.  I think the correct size is M2x3, and several M.2 SSDs come with the required screw anyway.  Then of course you'd need to either clone your spinning drive to your new SSD or just perform a clean install.

My Inspirion 15 7000 series 7559 has a built in SSD and a bay for a second hard drive.  Is there a new one that has that same option?  The problems with the 7559 range from flickering screen to failing usb ports.

My 15-7586 supports this option but as stated above, it must be ordered with the 3 cell battery as the 4 cell option doesn't include the bracket or the cable. I know this is an old thread but hope this helps anyone. I'm looking for a 14" 2 in 1 that supports dual storage drive options but so far no luck.

Why is this information so difficult to find? They know we like our upgrade-ability and still they elude us to simple fact based solutions. The best way that I have found so far is to research a buying option as close to what you are looking for and get the model number, then go to the support section and look at the pdf for set-up and configuration options and the service manual for information on the options which are available.

USUALLY , in the olden days, the trick was to find a laptop with a DVD drive, jank that one out, and replace it with an SSD-caddy, (preferably with an SSD inside of it .... of course ;-] ;-D )

But IDK if all Dells have the same connector for DVD drives that HP and Lenovo have. One would azzume yes......

Also, in a great example of "newer isn't always better", laptops don't even HAVE DVD drives anymore, so there's that.

OP had asked this in 2018

so you are trying to say that noone hasnt found or made any useful list of these in 4 years?:p

Here is s your Guide

Go to Dell.com 

Choose the series you wanna purchase (xps, inspiron) 

on left side you can choose the filters to find the configuration you are looking for 

Ability to a second SSD is not one of the choices for filters, here's your sign....  You have to call and talk to a human, some of them will know and some won't.