This power supply is available in 500 and 600 wattages, but the product I'm reviewing here is the 500 watt model (Model No. XF500, Part No. ULT31844). There is also an Active PFC 500W model which I hope to review at a later date. The continuous wattage on this power supply is more than ample power for most computer systems. Now how is this wattage determined? Well to understand that, you need to know what rails are.

Rails are basically well regulated transformers which convert domestic current into the voltages that your computer system can use. There are essentially two different rails: the 3.3/5v rail and the 12v rail. In this particular case, the approximate maximum peak output of the 3.3/5v rail is 160 watts and the 12v is 384 watts, which is essentially how the wattage of this power supply is determined.



The 3.3/5v rail is responsible for the motherboard, memory, PCI cards, AGP card and so on. The 12v rail is responsible for the HDD's, DVD, CD-ROM, fans, etc.

Also, some might be interested to know the peak amps on each rail. The +3.3V is 30A and the +5V is 30A. Unlike most power supplies with only one +12V rail, this product has two. The +12V1 is 16A and the +12V2 is 18A. NOTE: The 600W model has more amps on the +12V rails, but the 500W has more on the +3.3/5V rails.



This power supply meets ATX 12V v2.01 specifications. This basically means that a power supply must be able to sustain full load in 50 C (122 F) ambient conditions. Although, power output on all models will decrease ~1 C starting at an ambient temperature of 40 C. Having the ATX 12V v2.01 specification is important because some power supplies tend to overheat and shut down the system under max load. The efficiency is within specification and is 71% efficient at 500 watts. Higher end power supplies float in the ~85% range. Note that the more efficient a power supply is, the less heat is generated and therefore won't require excessive cooling.



I've been informed from Ultra Products that this product will be available with Active Power Factor Correction (APFC). Please note that this review sample does not have APFC. So, if you are interested in this product, keep in mind that in the near future another model will have this feature. Active PFC is preferred over Passive PFC because it provides more efficient power frequency. This reduces total harmonics, corrects input voltage, and it allows for a full input voltage range. The disadvantage is that it increases the cost of the power supply and tends to run hotter than a non-PFC unit at 115V. 

Additionally, this product is 100% Hi-pot, ATE (Automatic Test Equipment) & Burn-in function tested. What the heck does all that mean? Production Hi-pot testing ensures insulation integrity. In addition to being ATE tested, they bring a random sample back from the factory to the Taiwan office every day to get loaded on an ATE overnight. This is quite impressive. Finally, Burn-in is really a stress test and means it was tested at full load and still meets specs.

A power supply also needs to be fail-safe. This unit has Over Voltage Protection (OVP), Over Current Protection (OCP), Short Circuit Protection (SCP), and Over Temperature Protection (OTP).