Power Supply vs Adaptor

My DSL modem came with an adaptor. It burnt. I bought a new cheap adaptor, it burnt too and the next one too. So some one told be to buy a 9V DC power supply. He said unlike adaptors they dont get hot. Now I'm running my modem with a PS. It does get hot but not that much compared to the adaptors (the PS running my laptop doesn't get hot at all). However one good thing has happened. I dont get disconnected when a power failure occurs and my UPS kicks in. On adaptors I always disconnected. So what's the difference between an adaptor and PS? also on the PS the current mentioned is 1.1 Amp where as on adaptors it was 500 mA. So the current is double. What does it mean? And finally I've been told to not use adaptors with UPS because the normal average UPS doen't give correct voltages? Is that right?


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adaptors are powersupplies, powersupplies are adaptors.

the stronger the powersupply the more headroom (excess capability) there is, the excess capability is useful in extreme conditions. for this reason the 1,1A supply out-performs the 500mA supplies

the wall-wart type adaptors often have a simple transformer based design, and these transformers aren't designed to operate from the modified square wave output of a cheap UPS.

the brick style powersupplies (and some plug-adaptors) have a different design called switched mode which uses a special miniature transformer and high frequencies that is better suited to the UPS output.

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hope that helps.

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Jasen Betts

"Adaptor" is an extremely vague term. A wall-wart is just a PSU (power supply unit) built into the same case as the mains plug.

It means that you can draw twice as much current. If your modem used e.g.

400mA, the wall-wart would be operating at 80% of its limit, while the brick-style PSU would be operating at less than 40%. Like most things, PSUs will be more reliable if you leave some slack rather than pushing them to their limit.

Also, the 1.1A PSU probably has a larger output smoothing capacitor than the wall-wart, which is why you don't get disconnected by the brief power outage before the UPS kicks in.

A UPS typically puts out a very crude waveform, which puts additional "stress" on the PSU. If the PSU was operating close to its limit on mains, this may push it over the edge.

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