According to some of more intelligent people we know in the power supply business, making efficient power supplies is more difficult at lower wattage levels.  And while most power supply vendors were showing 80+ Gold rated PSUs for the first time (rated at 90% efficiency at 50% wattage level), Enermax was showing off a set of 450w, 550w and 650w models that will be available in Q3 of this year.

Computex 2009: Enermax shows 80+ Gold power supplies - Cases and Cooling  1

Computex 2009: Enermax shows 80+ Gold power supplies - Cases and Cooling  2

Enermax claims the secret to their ability to offer a low cost 80+ Gold PSU, something is easier to do with higher wattage, more expensive units, is the “dynamic hybrid transformer” seen here.  Due to the extreme secrecy between PSU companies, you can see that Enermax has actually blurred out the back of the unit to keep it from prying eyes. 

Regardless, you can be sure to find reviews of this PSU and other 80+ Gold units on PC Perspective very soon!