HardwareSecrets explains that rebranded power supplies aren't retested by Ecos Consulting, the company behind the 80Plus label:
Ecos Consulting offers a big discount when a company wants to get an 80 Plus certification for a rebranded power supply (instead of paying full price, they pay only 20% of the cost). They can reduce the price so much because they simply don’t test the new power supply. Since the power supply submitted for certification is a clone of another power supply already tested, and since identical power supplies will get the same results, Ecos Consulting simply doesn’t retest rebranded power supplies. So the discounted certification fee is in fact a fee for allowing the company to use the 80 Plus logo on the product and associated promotional material, and to generate a “new” test report that is an identical copy of the report of the original power supply, changing the product and company names, and adding a picture of the rebranded power supply..