Well it depends on what you have on the system, and what you plan to have.
Your CPU has a TDP of 95w, and the 560Ti has TDP of 210w, so that's 305w right there. Add in the mobo, two sticks of RAM, an SSD, an HDD and a third party cooler, and we're at 433w.
My own way of doing it is to get a PSU rated at 1.5x of the specced kit, to allow for headroom of efficiency, and potential future additions, which comes to 650w. Now bear in mind this is overhead to point of unnecessary, based on theoretical maximum power draw, but at least it stops at 650w.
However, if you're looking to move to another GPU at say 75w, 450w would be adequate. If staying with the 560Ti, I'd recommend 550w to 650w. I think I opted for a 750w on the basis that it was an extra tenner over the 650w, so why not.
Then there's the modular, semi-modular, non-modular aspect, which is really paying for less cables that aren't in use. That's up to you. If you want fully modular, you're talking £80-£120 realistically. If semi, then £60-£90. Poor cable management causes airflow issues, which creates more heat etc.
Then there's the 80+ ratings. I prefer Bronze as a minimum level of quality, but for any premium kit, I'd recommend gold or better.
Lastly, consider the warranty of any given model. Some are pretty good. I'd make sure the one you get is at least 5 years. You'll probably have to visit the specific site to find out the warranty. My PSU has 10 years.
Here's a good list of the different tiers to consider too (this separates models; not brands) - https://linustechtips.com/topic/1116640-psucultists-...
Here's a list of some PSUs that are lowish spec up to as much as you'll need. Selected brands and vendors, so play with the options - Linky
If you can, get a spec of your system built into the PC partpicker's system builder, so you can get an idea of the maximum wattages likely. Use a program like Speccy, or try the Userbenchmark to get the spec.
For the record, my cheap n cheerful browsing PC has a 430w Corsair CXM Bronze (semi) from 2015. It's ok, but the fan is a bit Meh. The gaming rig has a Seasonic 750 Focus Plus Gold (fully modular). It works. Zero complaints so far.