http://www.digitalgraphics.com.au/apc-ups.html (Serial Settings)
Settings are 8,0,1,Xon/Xoff
The APC SC 1500 UPS uses a very simple command language that is based around single characters and control characters. Apparently, USB interface is slightly buggy (could be software/firmware but apparently requires to re-attach cable every once in a while).
http://www.networkupstools.org/protocols/apcsmart.html (APC commands)
http://linux.die.net/man/8/apcupsd (APC control software)
While cheap the Upsonic Power PrOffice 650 seems to have configuration software available for it. It has an RS-232 interface and has Linux interfacing software.