[Re-posted with new subject and more appropriate NG's)

Using a USB-to-Serial adapter to connect a laptop to APC UPS' RS232 serial
port.

No signs of communication from the UPS. The laptop's OS has an
auto-recognition feature that enables built-in power-down options if/when the
UPS communicates its presence.

Loop-back test of the serial adapter confirms data is going out and coming
back, being displayed in a terminal program. (Local echo turned off.)

Serial cable (between adapter & UPS) is the correct APC p/n (with unique pin
assignments) for this application and model of UPS. Confirmed this with APC
tech support.

Tried power-cycling the UPS, and connecting the serial cable before & after.
No joy.

What options are left? This is a new (well, New, Old Stock) UPS and has not
seen any use before I powered it up last week.

Ideas?

Mac PowerBook; OS X 10.4.11
APC Backup-Pro 650 (model BP650S); APC serial cable #940-0095B
No-name USB-Serial adapter w/1.2.1r2 Prolific OS X driver

Thanks.