1. There is a large variation in the weight among the same wattage. For instance, among all the 300W power supplies, the weight ranged from 2.15 to 3.8lb, a 1.65lb difference. The lightest one is only 57% of the heaviest in weight. Among the 250W, the weight ranged from 1.7 to 3.1lb, a 1.4lb gap. The heaviest one is 82% heavier than the lightest one. Judging by these data, some of the good-quality 250W power supplies are clearly better than the poor-quality 300W’s. Therefore, don’t be fooled by the wattage on the sticker.
2. Generally, the Athlon-approved power supplies weigh more than the non-Athlon approved of the same wattage, confirming that Athlon-approved ones are of better quality. It's possible that manufacturers only submit better models for the AMD approval process.
3. The name-brand power supplies typically weigh more than the less-known, generic brands of the same wattage.
4. FCC approved power supplies often weigh more than those without FCC labeled.
5. Figure 1 clearly shows that the market price of the power supply is, to a degree, proportional to the weight, especially for items heavier than 2.25lb. The higher the weight, the higher the price tends to be. You pay for the pound! For power supplies weighing lower than 2.25lb (the blue dots), the correlation does not work well, suggesting either the existence of a minimum market value or some of these power supplies should be priced even lower (due to low quality).
6. Figure 2 shows that the wattage of a good-quality power supply is, to a degree, proportional to the weight for the good-quality power supplies such as Athlon approved 250W's and 300W's. This diagram also shows that some of the low-weight power supplies (blue dots) most likely do not have the true wattage as labeled.

Why Weight Matters?

The more appropriate question is why size matters.

The weight of a power supply is directly related to the quantity, quality, and size of the material (thus cost) used to build the power supply. We opened a light and a heavy 300W-labeled power supplies. The heavy one has larger capacitors, thicker wires, larger transformer, larger heat sinks, more connectors, and more capacitors than the light one, all of which are important factors for the overall cost and quality of a power supply. The difference is illustrated below:



Conclusions

This brief study clearly confirms an empirical knowledge: the quality of a power supply can be estimatd by its weight. While this is not a true scientific or thorough measurement of the power supply reliability, it is nevertheless a very simple and easy way for ordinary PC users to estimate and compare the quality of a power supply. Directron.com has pioneered this measurement and has now published the weights of all power supplies sold on Directron.com’s web site.

It’s important for the end-users to know the quality of a power supply. The specs of power supplies are simply printed on stickers. Don’t be fooled by them! The stickers can be easily removed and replaced. Even the manufacturers might place a 300W sticker on an otherwise 250W power supply. Once products are shipped it is quiet rare for any private or public entity to go back and verify the specs on the sticker. However, it’s difficult, if not impossible, for a dishonest vendor to alter the weight of a power supply.

By no means is the weight the best way to measure the quality of a power supply. There are other factors one should consider in purchasing a power supply such as wattage, output, brand, price, noise level, and long-term stability. However, to most end-users, measuring the weight may be the only viable method that's widely available.

The large variation in the quality of power supplies with identical wattage rating suggests that an industry agency is needed to rate, confirm, and police the labeling of power supplies to protect the consumers.

Table 2. A guideline to classify the quality of a power supply by its weight (lb).

Based on the above criteria and our general experience in return rates, these are consistently high quality brands on the market: EnerMax, Delta, PC Power & Cooling, Enhance, Antec, CWT, and SPI. These brands are consistently associated with low-eight models: L&C, Deer, Skyhawk, Star, KME, KingStar, and LCT. Our experience shows that the return rates of a low-weight power supply could be as high as twice of those of high-quality ones. How does your power supply measure up?

Physical Dimensions

Besides the specs and form factors, the physical dimensions are also important factors in selecting a compatible power supply. Here is an outline of the physical dimensions of most standard power supplies: