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I would like to understand the specific differences in power adapters that have similar input/output spec's but have different described purposes. In other words, can I use any power supply/adapter as long as the spec's are the same?

In this case, I have a hard disk system that has a supplied adapter that I suspect is bad. I have measured the voltage and it is within spec at 12.6Vdc. I do not know how to measure the amperage output without taking it apart, but I assume it is not outputting the needed amps because the hard disk enclosure does not start. So I want to first replace the power supply. Power supply is: Input: 100-240Vac Output: 12Vdc up to 6.67A

If I order one from the manufacturer, it is $70. But there are many LED and general system power adapters on Amazon that have specs like: Input: 100-240Vac Output: 12Vdc up to 8A

for about $20. So what am I purchasing for $70 versus $20? I understand the mfr would be more for their own costs, but they're OEMing the product as well.

So am I safe in getting a 12Vdc 8A output power adapter, like LED purposed or other, or is there some specific reasons I cannot do this?

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I would advice against LED-specific supplies since they are often constant current type. Another specialized type to avoid is one for battery charging. Check eBay for a replacement supply for your particular equipment; the supply could be generic but they often put a list of compatible equipment in the description.

The price is not very good indicator these days. Granted, for $70 you'll get a supply that is much less likely to give you grief. On the other hand, if you buy 3x$20 supplies from different places, two of them will be the same quality as the $70 one - and you save $10 :-).

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  • \$\begingroup\$ Thank you. I read the about constant current here, but need clarification of why that is bad for equipment like hard drives. If rated 8A, is an LED adapter constantly pushing full 8A? \$\endgroup\$ – mcheck Jan 14 '15 at 14:57
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Ac adapters are totally swappable. Just make sure it has the correct voltage and current ratings and go for it. Also need to make sure the connector matches, or you'll have to do some soldering.

It doesn't sound like the ac adapter is necessarily bad though, if it is outputting the correct voltage. I would hook the adapter up to a large power resistor and see if you can pull some amps out of it first. Be a shame to even spend 20 bucks if the issue is elsewhere.

edit: I agree with the other answer in that you should avoid adapters with specific uses like chargers or LED drivers, these tend to have additional circuitry that controls current.

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