easy upgrade to 280W.

https://www.dell.com/community/Optiplex-Desktops/upgrade-of-Optiplex-SFF-psu-to-280W-for-GTX1050-1050Ti/m-p/7536972#M40953

I think your 790 sff probably looks like this one https://cdn11.bigcommerce.com/s-h47f2g/images/stencil/500x659/products/7611/20332/1463099__50326.1517438039.jpg?c=2

and the sff in the video was optiplex 780 sff that looks like https://www.speedhelp.net/Bilder/Computer/P4/Dell/dell_op_780_sff/dell_optiplex_780_sff_4.jpg

yes there is a big change from 780 to 790 because the former uses BTX format motherboard and the latter ATX.  790 sff also uses standard ATX 24 pin.  

can you measure and send your sff psu physical dimensions?

Thank you for the response but unfortunately my power supply does not look like the one in the video. Mine is a long rectangle that is a 240w not a 235w if you can find another video or link for me that would be great! 

Hi @Dragon272, What GPU did you get?

Hi @redxps630, I couldn't immediately pull up dimensions on it, but might the Dell Vostro SFF 400w PSU also fit?

Hi thank you for being so kind, here is the dimensions of my psu 10.9 x 4.2 x 3.5 inches. Thank you so much for helping me.

Also I am am almost positive this is the psu that is in my optiplex 790 sff

https://www.amazon.com/Dell-Optiplex-desktop-H240AS-00-Computer/dp/B00ZR54C48

Hi I got a  MSI GT 1030 2GD4 LP OC Computer Graphics Cards. Thanks for all the help!

Wait..so is it fine for me to put that graphics card into a 240w battery? If so thank you so much for helping me. YOu are an amazing person!

there are Dell XE series psu that are long and look like the 790sff but they use proprietary 8 pin ATX connector, so can not be used in 790 sff.

the vostro 400W one physically will fit but can not be fastened to chassis so it will float inside.  similar psu dimensions are 3.4x2.5 inch. https://images-na.ssl-images-amazon.com/images/I/51yxcla9pZL._AC_.jpg

on the other hand I find some dell sff 275 w psu that may fit the 790 sff case, but it is only a modest enhancement of power.