Hi,

There are motherboards for 2 PSU's, even 3, like https://www.asus.com/Motherboards/B250-MINING-EXPERT/
Otherwise I would recommend a dual psu adapter, like http://www.thermaltake.com/Power_Supply/Accessories_/PSU_Cable/C_00002406/Dual_PSU_24Pin_Adapter_Cable/design.htm.
I hope this answers your quesionss.