With a fully modular PSU, you still get all the connectors you would on a non-modular ... you can check out our guide on how to check what PSU is in your PC. It can also help with the overall ...
Even if your old PSU can supply enough wattage for the latest graphics card, it might not physically support it due to newer power connectors on some of these graphics cards, such as the 12VHPWR ...