The iDRAC on the blade communicates with the CMC to determine power requirements. If the system will only allow you to power on a single blade at a time then my first guess would be that it has determined you only have enough power for a single blade. Check the CMC logs to see if more information is listed on the reason it will not power on the blade.
There are several factors that affect available power. The wattage of the power supplies, number of power supplies, power supply mode, and input voltage all affect available power. I suggest reviewing your power subsystem to see if it is being limited. You can find documentation on the system on the VRTX support page. It should be under servers>poweredge>modular infrastructure.
Dell EMC, Enterprise Engineer
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