perhaps like the one in this auction for a Wurlitzer?
http://www.ebay.com/itm/121072536510
thanks
Jim
On 3/18/2013 1:36 PM, Richard wrote:
  OK, I've got an HP X-Y display with the older
power cord connector,
 where the three pins are round instead of two being blades and the
 only the ground pin being round.  The entire plug socket is also
 rounded instead of angled.
 I've tried to find a relevant picture on the interwebs, but you try
 googling "power coord connector" sometime and see if you can find the
 older oddball you're looking for...
 Hopefully my description alone is enough to aid someone in identifying
 the exact standard/specification for this kind of connector.
 I'm looking for cords that fit the connector.  I will try to remember
 to take a picture with my phone on Wednesday when I am down at the
 museum, if we can't figure it out by then.