It depends on the card model and your power supply. Some GTX 750 TI models require supplemental PCI power connections, some don't. If you have an OEM power supply and your card model you are looking at needs PCI power, rather than only getting power through the motherboard slot, then it won't work. If you have a low end OEM power supply, even without the need for supplemental power it's highly recommended to upgrade the power supply.
If you are using the OEM power supply that came with your computer it's recommended to not go higher than a GTX 750 on the green team or a R7 250 on the red team.