Yes a crisis! Reg. RNDX4000 with defect PSU

You cannot simply move your drives from an NVX to a current OS6 NAS and use it.  But, you can use the current unit to access the data (as read-only, and assuming the volume was not damaged by the power failure) and transfer it to a backup.  Then, you can re-format the drives in the new NAS's file system and restore the data from the backup.

I agree with you that fixing an NVX is probably not worth the effort and cost unless you have another compatible NAS (like an NV+ V1) from which you can "steal" the supply.  But, you can make an inexpensive cable to allow you to connect a standard ATX supply externally so you can access the files.  The ReadyNAS pin-out is slightly modified from the standard ATX: ReadyNAS_PSU_pinout.pdf .  If you want to put new drives in your new NAS, this will allow you to transfer the files NAS-to-NAS without the intermediary backup device.

But, you really should implement backup, so this is an opportunity to do so.  As you have discovered, RAID is not a cure-all for potential data loss.  Only real (in a separate device) backup can fully protect you, and even that has to be off site to insure fire, flood, or theft don't cause you to lose both.