No it won't work. Optiplex models have very small power supply--well under 300 watts-- and very small cases depending on which model 790.  Large size video cards will not fit and need large power supply units. Remember that Optiplex models are for business use and are not recommended for gaming and are difficult if not impossible to upgrade. Look for a low powered low profile older video card and check to see if your version of the 790 even  has a slot for a discrete card. The 790 model is 8 years old now. See the specs--

https://i.dell.com/sites/csdocuments/Shared-Content_data-Sheets_Documents/en/us/optiplex-790-customer-brochure.pdf

From the specs for the card you listed-- • Reminder: GTX 950  video card requires 450 W power supply 

I have a gtx1050 in my 780.

Case size isn't listed.  Listing it speeds troubleshooting.  Is your 790 an MT, DT, SFF, or USFF?  USFF's have no expansion card slots.

The GT 1030 is regularly recommended for Optiplex's by one of our Rockstars.  However, it would still help to know the case size.

I think this is the one he usually links:

https://www.dell.com/en-us/work/shop/pny-geforce-gt-1030-graphics-card-2-gb-gddr5-low-profile/apd/a9763687/graphic-video-cards

Looks like dell sells the PNY branded card. I notice that there are lots of makers gigabyte, msi, evga and I wonder if they all work about the same, or if some are a bad idea? Some seem to have a fan, others claim they are passive.

I saw these on ebay:

https://www.ebay.com/sch/i.html?_from=R40&_nkw=gt+1030+low+profile+gddr5&_sacat=0&_sop=15

There were no PNY listed when I looked, strange.