I'm using the PSU from a ZIP100 parallel drive with a new plug on end. 5VDC @ 2A. It's a xfmr based wall wart and I've been using for ~1yr with no problems charging or grd loops when used with AC powered headphone amp. Gives the "Charge Complete" message when fully charged. Probably find these at thrift stores and such. I always take a multimeter with me and plug them in and make sure they work b4 I buy.
www.isellsurplus.com has these for just under $13USD last itme I looked. Use the RS plug mentioned in an earlier post and you're good to go.