There are a number of things to consider for a power supply... apart from just it's rated output. Different manufacturers may use lower quality components that don't regulate that output as well. For example, a power supply designed for something like a portable CD player (or similar device) may not have the strictest control on voltage fluctuations. Something like a portable CD player is probably much more tolerant of varying input voltages (to a degree). There is also the issue of how "clean" the power is, grounding, etc. Noise in the power going to something like a CD player isn't really going to generally impact the devices performance. When you're talking about something like a notebook, you want to be sure your power supply is the highest quality... not the cheapest available. All power supplies are not created equal. In general, you'll find that all notebook power supplies are much more expensive than a generic power supply that just provides the same output voltage/wattage. While third party chargers are often less expensive than the original manufacturers, they are still not cheap and generally run in the $60 and up range (from companies like Kensington and Targus). Your notebook is too valuable to to risk its safety by saving a few $$ on a generic charger... especially one which is basically a "cut & tape" job. You have no way of knowing if they have configured the connections to the MagSafe correctly (there are more than just two wires involved).