Power supply usage?

I have Rm750 crosair power-supply, it has a capacity of 750 watt. I currently have HS(235 watt) box and CK (220 watt) box running on it. Can I add more goldshell boxes to it?

You should not add more. To be safe, you should not use more than 80% of the rated power. So 750 watt power supply should not have more than 600 watts pulling from it. So if you add another similar miner, you would be over 600 watts.

Thank you so much for the advice!

Which power supply do you use?

I am using a corsair 80plus gold 850 watt, which means the most watts I should pull from it safely is 680. Also, on the goldshell website, they specify their wattages for each unit and then it also normally shows ±5%. So if it says 200 watts for a miner, plan on it pulling 210 watts in your calculations.