You where the one that said that rtx cards need a certain uefi thingy, how do i fix that or mod it on the motherboard?

larger cards need bigger power supply.

Cards up to and including 1080 ti work fine in machines with enough power and physical space like the 2006 XPS 400.

https://www.youtube.com/watch?v=qa9b0TkTsLM

So it works on an optiplex 790  with 700w psu? OK, ill prob remove the gpu shroud if it doesnt fit

And a 1070 ti or 1080 non ti work?

Here's what I can answer.

Check your CPU against the GPU you want for bottleneck..  For example, if you have an I7-2600, in Google, key in "I7-2600 GTX 1070 ti bottleneck."  Click on the option that's PC Builds bottleneck calculator.  Result is in the screengrab:

You may have gotten ahead of yourself with centering around the 1070 ti & 1080 ti.  If one of those is what you really want, then I'd have to suggest a PC with a much more advanced CPU.

I just want the 1070 ti  to keep for my new pc that im building in a year or so, so I can already have a gpu for that and have it work for a couple more years, my current dell is probably gonna be retired in a year

So basically I really don't care about bottlenecking, I just want a card that I can use for much longer and btw I have the i5 2500

I just want to know more also about the rtx incompaitibility,

"speedstep" said that rtx cards are not compatible

https://www.dell.com/community/Optiplex-Desktops/best-gpu-for-desktop-optiplex-790/td-p/7347169

They said

"GTX 2080 cards are not working for the same reason Radeon R series cards don't work.  They Require UEFI ACPI 2.0 windows 10 class 2.3.1 bios."

and I wanna know if I can fix that because I heard rtx prices are going down on ebay

So if I get an rtx card, I know it will bottleneck more, but I wanna be able to use it for a few more years

but it might not bottleneck that hard

austin evans made a video paring the athlon 3000g with rtx 2080 ti

https://www.youtube.com/watch?v=dhGZgWcQDM8

and their bottleneck wasnt that bad, and an athlom 3000g has lower specs than i5 2500

Class 1 doest support any UEFI features its in Legacy Mode all the time.

You cannot add

Class 2.3.1  UEFI secure boot to a 790

https://docs.microsoft.com/en-us/windows-hardware/design/device-experiences/oem-uefi

End users cannot add Microsoft Certificates or win8 or win10 bios Windows keys to systems that allow 32 bit XP and other legacy OS.

This is NEVER an option.

UEFI classes

• Class 0: Legacy BIOS
• Class 1.00: UEFI in CSM-only mode (i.e. no UEFI booting)
• Class 2.3.1: UEFI with CSM
• Class 3.00: UEFI without CSM

https://uefi.org/sites/default/files/resources/Brian_Richardson_Intel_Final.pdf

BIOS CLASSES

Will a 1070ti work well in The 790 with a I5 2400?

@jmoneyjrock ,

Not exactly.  See screengrab.  Plus you'd have to upgrade PSU.

Also, what size is your 790?