As long as your motherboard has a PCI-Express x16 slot, it will fit, but your 250W PSU is too weak for that card, you'll only cause it to explode when you try turning on your PC with this card. Time to upgrade the PSU first before you can even think about upgrading the GPU. 250W.....haven't seen nor gamed on those since an Intel PIII PC and FX 5200 256MB rig I had back in High school nearly 13 years ago now, lol.
To use that card, you will need a good quality 400W+ PSU or at least a 500W+ cheapo no name Chinese junk PSU to be safe.