RX 550 in a vostro 260

that should work.  I can not find user validation of V260 and Radeon RX gpu but a similar Optiplex 790 with intel 2nd gen cpu like 260 are validated to work with RX 550

@redxps630​ would it work well with the i7 2600?

well depends on what your objectives are.  It is not a high end gpu for sure.

there are other gpu that match i7-2600 and are suitable for gaming.

for example The Nvidia GTX 1060 6gb for 1080p resolution and the Nvidia gtx 1080 for 1440p resolution,  any of the GTX 16xx cards, and also RX580 which is much more powerful than RX 550 (250% faster).  all these require a psu update.

even the GTX 1050 is 80% faster than RX 550

RX 550 is for someone sitting in the office or home doing mostly office work and want some occasional light gaming.  do not expect it to be much.

@redxps630​ I've tried to use some other gpu's like the RX 580, but I couldn't use them due to the size constraint, so I decided to try the RX 550. Are there any other decently cheap low profile GPU's I could use?

you can try GTX 1050 low profile.

Dell makes an RX640 low profile card. Its a essentially an RX550 low profile but more efficient uses less power.

https://www.techpowerup.com/gpu-specs/radeon-rx-640-oem.c4110