Need help with dell specific PSU

Lets clean up right at the beginning the obvious question. “Why a dell if you want to upgrade?” And the answer is i did not chose a dell, but an asus. Long story short supplier couldnt get enough so they substituted dell inspiron 3891 for the missing part.
Mine is equipped with a 360W HU360EBM-00 PSU. Here is the issue, i want to keep my current gpu (vega64) but it sips up 300W in itself so it would make short work of this PSU’s OCP/OPP.
Im assuming dell uses the same 12vo mobo connector across more models so id like to ask if anyone knows about a bigger psu (preferably 500W min) that would work in this machine?

As a plan B i have a dual PSU setup where a relay powered from the pc shorts the 2nd PSU’s atx connector to turn on and give power to the GPU but im not sure if its safe to do it this way…

(Last resort: passive cable that permanently turns on atx PSU and converts it to the dell connector. Ill have to turn off PSU manually in this case.)