I checked "Belarc" for the computer but couldn't find a listing for the Power Supply. The only visible tag on the power supply is DP/N OM1J3H.
What I have a question about is what part of a USB circuit draws significant wattage. Each of the HD caddies has it's own power supply which I assume handles the spin part of the drive but not the bits and bytes. If the wattage drawn by the PC board and caddy circuits is small (compared to the power supply wattage) then the problem might be in the USB path and voltage drops along the way rather than wattage
At this point I have disconnected the caddies and intend to use them only when I update backups to them. I also shortened up the USB cables from 6 ft to 3 ft. I'm using the 3 internal HD drives for daily work.