I replaced the hard disk in my Tyros4 with an SSD.
I now have the old T4 hard disk in an external USB disk enclosure.
I can plug this into the T4 and it works fine, even without any external power. Some disks will use more power than others, especially when first spinning up, so the fact that this disk works on my T4 does not mean that every one will!
I also think that the Tyros models use a different USB power controller chip than the PSRs, so maybe they can supply a bit more current, but to conform to the USB 2.0 standard, any sockets should be able to supply 500 mA.
Regards
Ian