It's normal. That psu is not the top product and it is not made for doing such things. It is meant for normal use not minging purposes.
If you are running at around or above 300W which you probaby are,... eh I would rather spare ~`100€ and bought something better.
Sooner or later it will die.
I believe I am fine and now it's not that hot anymore, I don't know what happened yesterday but now is running just warm which is normal for a PSU.
By the way I am not running above 300W, 160W are both 1060 cards as I have toned down them to 70% power limit maximum and the board is with SSD and DDR4 ram so I am sure it is not more than 90 W in total and in total I am only doing 250 W which should be pretty easy to handle from a really good PSU 550 W.