Getting your hands on a brand new RTX 4070 Ti would be awesome, but it's important to make sure your system has a power supply with enough capacity to actually support it. Since the 4070 Ti is rated for a maximum power draw of 285W, it's best paired with a 750W PSU. A power supply of this caliber will give the graphics card the juice it needs for maximum performance while also providing enough power for other components like your CPU and RAM modules.
If you need to upgrade your PC's PSU, you'll be happy to know that even the best power supply units aren't terribly expensive. You'll have no problem finding a quality PSU that falls in the $100-150 range, provided you're not looking at power supplies with extremely high 1000W+ capacities.