The small body size of the RX series power supplies may leave you deceived as to it's fan size. What looks like a 120mm fan is actually slightly larger, it's a 135mm fan. To keep nosy fingers out, the wire fan grill is painted to match the chassis. This fan is rated at a minimum of 15.5dBA for both models and the Nexus graphs show it going to around 30dBA at full load. The official graph is provided below:

As I just mentioned, the body of the RX series does seem rather shallow for it being a modular supply. Most modular power supplies are known for having longer bodies to accommodate the internal connections and wiring for the modular design. However, the RX series isn't much longer than a standard hard-wired power supply body. This will make it a great contender for smaller cases and HTPC cases because it will allow for better airflow in these usually cramped designs. The modular connectors are grouped into two groups; the two yellow ones are for PCI-Express and the other six are for peripheral connectors. All the modular cables use the same six-pin design at the power supply end. The sleeving of these cables is also eye-catching, it's black with crisscrossing white lines down it's length for some nice contrast. The layout of these cables is as follows:

(Click below to enlarge)
 

Nexus says both the RX-5300 and RX-6300 have a "guaranteed minimum efficiency" of 82% or higher. When I see advertised efficiencies I do what most consumers would do; I start searching the box for the official 80PLUS certification logo. A power supply with 82% or above would fall into the 80PLUS Bronze category. Interestingly enough, you will not find an 80PLUS logo on any Nexus power supply boxes. Being curious about this, I decided to send an email back to my rep at Nexus to see what the story behind this is. He told me that they found that when they had two of their older power supplies 80PLUS certified that it barely changed their sales numbers. Since having a power supply 80PLUS certified requires them paying an amount of money to the 80PLUS organization, they did not want to raise the price of the supply higher to accommodate this. Also, Nexus is a company based out of Europe and the 80PLUS organization is not as well known over there as it is in North America.

The entire RX series of power supplies are Active PFC so the power supply is using the power it takes in more efficiently. When paying extra to get a good quality power supply, you should always make sure it has Active PFC. I think the best explanation of this feature comes directly from Nexus:

"Power Factor Correction (PFC) allows the power distribution system to operate at maximum efficiency. This does not so much influence your electricity bill but it will also reduce energy consumption at the side of the power provider so it is contributing to using our planets resources better and more carefull. Active PFC is technically more complex then passive PFC and matches the overall high quality standard and reliability of this Nexus power supplies."