The bridge I'd use is from Anker, and you can get those off Amazon either without or with a power supply. The power supply is 12VDC 2 amps (24 watts), and creating a power cable and plug from the 12VDC power ports (SATA or 4-pin Molex) would be easy.
I'm thinking that 2 amps of 12VDC is more than enough to run a multi-Terabyte HDD.... I checked and some 5TB HDDs I found ran in use at about 10 watts. Even drawing power to the bridge off a spare floppy power cable, which has its 12VDC wire rated for 3 amps, that would be more than enough wattage (36 watts) to easily power a large HDD.
https://www.amazon.com/Anker-Converter-Adapter-Cable-included/dp/B005B3VO24
EDIT: Looking deeper, here is a SIIG one that specifies the chipset from ASMedia for the bridge, which allows SATA III performance. The xw generation of HP workstations are SATA II, however, but this would be backwards compatible. These adapters all can run a 2.5" drive off USB3 bus power, but for 3.5" drives they need the supplemental 12VDC. The SIIG site specifically states that their bridge supports 4TB drives:
I do not have experience with plug-in PCIe SATA II or III interface cards, so that remains an avenue for your added research. Those are now inexpensive enough that it might be worth doing the experiment to see, and please let us know your results.
Finally, I have posted in this forum recently on the ESB2 drivers from Intel variably supporting the TRIM feature that W7/W10 uses to keep SSDs tuned up automatically. If you are running a SSD in any of these xw workstations this is quite important for you to read up on, HERE .