W800RF32A USB: Their USB -> Serial adapter cable or Keyspan? - Spoke too soon?

[Jeffrey Lomicka]

The 40 watt rule is only for those units (usually simple switches) 
that don't have access to "white wire" power, and are getting their 
power through the filament of the lamp.  The plug-in modules and 
modules that require a neutral lead won't have trouble with a 25 
watt, 7 watt, or even a 4 watt Christmas window lamp as their only 
load.