Hi
If I connect a gpu to a cable pcie of a psu and the riser with a cable of a different psu, can it be a problem?
Apologies for my bad command of english.
Don't do that, unless your psu are hybrid support. read and educate yourself about it on google first. For starters, this seems highly unsafe to me.
Edit: I had googled about powering your mobo with different gpus and powering your gpu with different, and you were advised to not.