Please help me, it's about graphics cards.

The 790DT has a 250W PSU. The GT710 minimum PSU requirement is 300W. It might work but it is pushing the power supply on an almost 8 year old system. There are 400W PSUs available on the Internet for the 790DT and with that upgrade you could go to a GTX 1050 or even a GTX 1060. For a system that is getting up there in age, the point is do you want to spend money for a PSU and GPU upgrade or put that money toward a new unit.

would this work????

https://trademe.nz/marketplace/computers/components/cases-power-supplies/power-supplies/listing/1885819195

because i dont know what fits and what doesnt, i dont build computers.

If you are intimidated, do not even try it. Possibly a local tech shop can help..

https://www.dell.com/community/Optiplex-Desktops/What-psu-do-i-need-for-a-dell-optiplex-790-mt/td-p/6037403

;/ i might just buy somethingthe card i want is 90 dollars and my budget for the psu would be 10 (again nzd)

would a HD 5970 work? with a 250w psu (Please note I'll only be playing roblox and minecraft. )

From the 790 Tech Guide:  1GB AMD RADEON HD 6450 with DP and DVI; 512MB AMD RADEON HD 6350 with dual DVI or dual VGA (adapters convert to dual DVI or dual VGA)

This is for the MT, DT, SFF, and Not the USFF.

so should i get that card that you just said?

Please help me as well ! I have an old system DELL Precision 1600 with Pentium G840 2.8 Ghz ,Will the said card Gtx 1030 Will work on system efficiently . IF not what other budget card should i buy ? I have no idea which is compatible with my machine . 

I HAVE 790

AND ANTHING WORKS, THERE.

my 700watt PSU assures that,(upgraded it)

but sure that old card slow works,  it uses no power at all to speak.

here is what works on my 790

R9-380 (uses lots of power) 190w

GTX750, gtx 1050, GTS260 power hog extreme 200w,  and all old cards back to year 2001. PCI-E

R5-240 Radeon (November 1, 2013)

and more tried over 20 cards, in mY  790 MT

any card will work if it don't hit

learn that there are vast numbers of makers 20:? and lots of form factors , Low profile is less choices but length and fan count and noise tops the list.

• must fit and not hit, (use a ruler is best) Some cards hit card cage, or  even hit power jack 24 or SATA cables.  only looking first works ok?  first is the cards spec, then ruler used inside the PC.
• power PSU demands, I have none but you do.
• slot limits, mine has none but 75w on the slot, max.  (not 25w limited like some dells are)
• OS will be happy,  no problems there.

the DT is Height challenged.

IF you buy card too long it hits this blue thing HDD caddy

if you buy a card too wide it hits this silly tiny weak PSU,.  the space is limited, next time by real PC the MT.

DT ONLY 790

wrong arrow sorry

here is a real; 790 MT GPU card 260 hitting the SATA PORTs

there is no card 3D forum factor standards, at all, sure tall, (but only kinda)

Some full height cards are too tall for DELL MT cases even. (I cured that too)

the faster cards have bigger and sometime deeper fans that hits things.  (so FIT IS FIRST)

7750 is a 75W card that requires 300W minimum power supply. 

Low Profile HD5450 would work because its a 27W card.

GT 1030 works because its a 40W max card.

400W power man power supply DOES NOT HAVE 150W on the 3.3v/5v rails combined so its not working ever.

FULL SIZE power supplies DO NOT PHYSICALLY FIT into Desktop and SFF Cases.