XPG 750W + Seasonic 850W doesnt work together

[SSEmre]

I have a XPG Core Reactor 750w. This PSU feeding 2x RTX3080 + motherboard + 2 riser. Im tried add a Seasonic 850FX with add2psu adapter but doesnt work. Im using 24 pin jumper for seasonic and now works. Seasonic only feeding 1x Radeon VII + riser. 24 pin jumper is safe for dual PSU ? And why PSUs doesnt work in add2psu adapter?

[rdluffy]

Most likely the problem is add2psu with some defect
add2psu is good because fits better, no need to plug or unplug, just turn on your primary psu and you'll be good
But any jumper will work equally, a paper clip or any piece of cable, I used for some time and there's no problem, it's safe, the downside is to have to turn the second PSU at the same time as first one

But the add2psu is cheap, try another one, as I said it's probably a defect on this piece, because there's no such thing like PSUs incompatibilty