Actually no IBM M has a >500mA inrush draw so

-Not all converters support it

-Some converters that support it, are disabled by the motherboard as the converter is exceeding spec.

    but valarauca why don't you use an externally powered hub?

I've actually tired 4 different models, none have worked. I've just accepted that using a PS/2 plug on the motherboard is less of a head ache.

I do have a PS/2 -> USB converter that works, but only with 1 of my motherboards (a VIA). Except it knocks out the other USB port stacked above/below it. I don't plug anything into that port for the PS/2 -> USB converter, just that port will never recognize something is plugged into it. I think it is a power draw issue.