There is no GTX 950Ti, just a 950. A 240 watt PSU is too low to run it, you need a 320 watt or higher good quality PSU with a 6 pin PCIe power cable. If you have a small form case it won't fit a full size card.
A GT730 GDDR5 may be good to use in that system, just make sure you do a BIOS update. You will be running games on low quality and for newer games will probably have to run them at 720 resolution. 1030 may work, but those new card may have issues booting on older systems so may be safer to go with a 730.