When trying to power on a virtual machine, VMware vCenter will give the following error:
vCenter was unable to find a suitable host to power on the virtual machine for the reasons listed below.
DRS cannot find a host to power on or migrate the virtual machine.
It will then give specific details about each host and why vCenter was unable to power on the virtual machine for each host. Typically these are because there is either insufficient capacity on each physical CPU or insufficient memory capacity.
To fix this, either increase the hardware capacity as appropriate or edit the virtual machine (Right click -> Edit Settings…) and reduce the reservation (on the Resources tab) of the resource that is of insufficient capacity to power on the virtual machine.