Thanks JOcean.

Anybody, I also want to upgrade the RAM, using Crucials site for compatability. Should I be concerned about Secure Boot while replacing RAM Modules, or even adding the second drive? Somethiong about non Dell cards creating issues.

Yes, if your OS Drive is encrypted disabling secureboot is recommended. 

Any hardware change can trigger windows bit locker.

If your hard drive is not Encrypted and it won't matter, as it can be toggled after installing the parts too. 

Open DISK management and C Drive will show ,Encrypted or nothing

Hi,

I want also to add a second drive in my inspiron 5400 AIO. I have already a M2 in it and I want to add a SSD also, because I have the sata connection for it. My issue is that I don't have the bracket for it (SSD support). I tried with many others but are not compatible. Does anyone have any referance about it or from where I can buy one? Thanks in advance. 

Same here. I ended up just installing the ssd without the bracket and hoping it doesn't fall out.

There are two small brackets already waiting for you on the inside of the computer. With the back off you can find them on the upper left side clipped into the frame. You'll need four m3 screws to connect them to your SSD and then another two to secure them in place on the internal frame.