A graphics card that will fit in a dell optiplex 780 dt without external power needed

Solution
Either LP 750 or 740 should fit but yes it is tight. Also they are getting to be quite uncommon these days. I don't think they are in production anymore so the ones you find are just leftovers.
That may not be so easy. Those type of desktops are not meant for adding extra accessories. Your best bet is either the RX 460 or GTX 1050 as they both draw power from the motherboard. However, without knowing the case, motherboard, and CPU specs, it may be a bit tough.
 

Rogue Leader

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Neither of those GPUs are available in half height, and both require more power than that PC's PSU can put out.



The GTX 750 has 2 half height options, both should work but are hard to come by these days, also the GT 740 is a good common choice as its low power. Anything else will not fit and will draw too much power. Its a common upgrade to that type of PC.

 


Thanks for that. Still though, that case is going to be tough.