2 PSU's questions

I'm going to build my rig with 2 650W PSU's.

I would connect 3 gpus with 6+2PCIE power connectors and the rizers with 3 molex from one psu, and the other 3 gpus/rizers + the motherboard with the second PSU.

Do I really need this to join them together or does it also work without this connector?
Add2PSU Multiple Power Supply Adapter - https://www.amazon.com/Add2PSU-Multiple-Power-Supply-Adapter/dp/B009P98Q8U