Trouble is that my lappy has only 3 USB ports, 2 tightly together on L and 1 isolated on R, and I occasionally need 3 USB devices, the HDD caddy, mouse dongle & flash drive. The ports on L are so close that, with the caddy's Type A USB plugged in, the thicker flash drive has no room to fit, only the dongle will.
The caddy contains electronic gubbins to convert SATA to USB (propriety) output from whence about a 18" cable goes to PC USB port.
Which bit is likely to be faulty?. It'll be either the USB cable/plug or the caddy's electronics; not the drive cuz that's works any way. I would put my money on the cable itself as the electronics would seem too far away.