Hello SDH, I can confirm that I have a 600W as a power supply, I have attached the image of the label.Unfortunately, at the level of PCIe cables there is only the G1.
I noticed among other things that looking at the ads on ebay about the 600W power supply, some seem (as evidenced by the photos you see), as in my case only the G1, others seem to have them both.
https://www.ebay.it/sch/i.html?_from=R40&_trksid=m570.l1313&_nkw=Z420+power+supply+600&_sacat=0
I was thinking, is not that the seller (I bought from workstation4u) from where I took the workstation, may have "removed" the G2 cable?