UPnP compared to Port Address Translation

[Tim Callaghan]

I'm looking to purchase an inexpensive router (with wireless) for my
office to backup the firewall (in case the firewall goes down).

I need the device to support Port Address Translation (PAT) so I can
create rules like sending all TCP Port 26 Traffic to an internal IP of
192.168.0.51 on Port 25.

Many new devices do not mention PAT but talk about supporting UPnP,
which looks quite similar to PAT. I spoke with LinkSys technical
support but the engineer didn't even come close to answering my
question about the differences.

Can someone let me know if UPnP is just a fancy name for PAT or if
it's something entirely different?

Thanks,
Tim