Low noise (noise killer)
This means that the speed of the PSU fan is varied depending on temperature or, less often, on load power. This speed management is currently implemented in all PSUs, even cheapest ones, so the question is about the quality of implementation. This quality can be viewed from three aspects: the quality of the employed fan, the minimum speed of the fan, and the speed adjustment range. For example, simplest power supplies may have speed management, but the speed is changed from 2500rpm at a 50W load to 2700rpm at a 350W load. It’s like the speed doesn’t change at all.
Respectable manufacturers implement the fan speed management system properly, but often play another marketing trick. The fan speed (or the noise level) they write into the power supply specs is measured at a temperature of 18°C as reported by a sensor inside the PSU. This thermal sensor is usually installed somewhere in the hottest part of the PSU, on the heatsink with diode packs, so you can only have that temperature in reality if you put your PSU in a refrigerator. Although no one keeps PSUs in a fridge, the specification still contains an unrealistically pretty number like a noise level of 16dBA (this is quieter than the background noise in a quiet room). In reality, the room temperature is usually within 20-25°C, and the temperature inside the PC case is closer to 30°C. Of course, you can’t get 16dBA under such conditions.
Short circuit protection (SCP)
Short circuit protection is obligatory according to the ATX12V Power Supply Design Guide. This means that it is implemented in all power supplies, even those that don’t explicitly mention such protection, that claim to comply with that standard.
Overpower (overload) protection (OPP)
This protects the power supply from overload on all of its outputs combined. This protection is obligatory.
Overcurrent protection (OCP)
This protects the separate PSU outputs from overload (but not yet from short circuit). It is available on many, but not all, PSUs, and not for all of the outputs. This protection is not obligatory.
Overtemperature protection (OTP)
This protects the PSU from overheat. It is not required and is not implemented often.
Overvoltage protection (OVP)
This protection is obligatory, but is only meant for critical failures. It works only when some output voltage shoots 20-25% above the nominal value. In other words, if your power supply yields 13V instead of 12V, you must replace it as soon as possible, but its protection is not required to react yet because it is designed for even more critical situations.
Undervoltage protection (UVP)
As opposed to too-high voltage, too-low voltage cannot do much harm to your computer, but may cause failures in operation of the hard drive, for example. This protection works when a voltage bottoms out by 20-25%.
Soft braided nylon tubes on the PSU’s output cables help lay them out neatly inside the system case.
Unfortunately, many manufacturers have switched from the undoubtedly good idea of using nylon sleeves to the use of thick plastic tubes, often screened and covered with a paint that shines in ultraviolet. The shining paint is a matter of personal taste, of course, but the screening does not do anything good to the PSU cables. The thick tubes make the cables stiff and unwilling to bend, which makes it hard to lay them out in the system case properly and is even dangerous for the power connectors that have to bear the pressure of the cables that resist the bending.
This is often advertised as a means to improve the cooling of the system case, but I can assure you that the tubes on the power cables have but a very small effect on the airflows inside your computer.