Yes you can run 2 GPUs with that split-end cable. However...
Make sure you put GPUs close enough so the length is long enough
After a few hours touch the end of the cable going into the modular PSU and make sure its not burning hot. Sometimes there is a bad connection and they will melt.
Ok I just got the new gpu and connected them that way.
I'll keep an eye on that cable as you said and hopefully it won't burn or something *fingers crossed*
All of your questions depend upon what cards you have.
As a rule of thumb, nvidia cards use less power than AMD cards. What cards exactly are you using with this rig?
You'll also want to find out the power usage of your entire system. I use pcpartpicker for this. Most mobo+CPU+ram combos come out between 110W-150W... some CPUs use a lot more though.
Oh they're nvidia cards. To be specific they're gtx 1060s. And I just got to that site and in theory I can use 4 gpus but it's kinda risky.
The system without any gpus uses about 140w. And each card about 120w.
So (120*4 ) + 140= 620w.
And it should be able to handle 750w right ?
But I was told that I shouldn't try to push the PSU to the limit. So I'll buy another 750 or 850 one to be safe.