To be precise, and I do love being precise, the dummy load is not what provides the -5V supply.
A dummy load is placed on the 12V rail because most modern power supplies expect to be most heavily loaded on the 12V rail. Older computers drew more heavily on the 3.3V and 5V rails. Some power supplies will use a DC to DC converter to derive 5V and 3.3V from the 12V, which is usually sufficient to load the 12V rail satisfactorily enough to get correct voltages being produced. For those that don't, the dummy load helps to stabilise the voltage regulation by adding a load to the 12V.
The -5V is usually something that will step down -12V to create -5V.
All that to say that the eBay seller provides multiple options, so you need to know that a dummy load does not equal the provision of -5V.
This all becomes less important given that, as mentioned above, the Sound Blaster Pro 2 does not need -5V, but the Sound Blaster 2.0 does.
MT-32 Old, CM-32L, CM-500, SC-55mkII, SC-88Pro, SC-D70, FB-01, MU2000EX
K6-III+/450/GA-5AX/G400 Max/Voodoo2 SLI/CT1750/MPU-401AT/Audigy 2ZS
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