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Two 12V AC/DC adapters, one much heavier than the other

I was browsing the thrift store and found a nice pair of JBL 2.0 computer speakers, but they lacked a power adapter. They call for a 12V 1A supply. I have a ton of "bricks" lying around, but no 12V ones to spare (if it's possible and economical to turn a 5V 3A brick into a 12V 1A+, please point me in the right direction). At the store I bought a cheap router that included the one on the left, but it's very light. I envisioned the necessary adapter to be very heavy, as any older computer speakers I've seen had a heavy brick, so I kept looking and found the one on the right sold individually. It's got to weigh 5x as much, but the specs look similar (I understand it's only 700mA and that means I can't draw as much power). If neither is a good fit I'd rather purchase a new one than chance it, but this got me thinking:

What's the difference between these two types of adapters?

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  • \$\begingroup\$ The right one is a linear power supply, the left is a switching power supply. Older adapters were linear, with switching power supply the transformer in the adapter can be smaller. \$\endgroup\$
    – I. Wolfe
    Commented Mar 14, 2015 at 1:53

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A "heavy" power supply contains a 50/60 Hz transformer to provide the necessary isolation between the mains and the DC output. This transformer has a laminated steel core that needs to be fairly massive in order to provide an adequate impedance to the line voltage.

A "light" power supply uses active electronics to convert the line frequency to a much higher frequency (on the order of 20 to 100 kHz). This allows the isolation to be achieved with a much smaller transformer that has a powdered ferrite core.

As long as the output ratings are compatible (same voltage, same or higher current rating), they're mostly interchangeable. Beware of the difference between regulated and unregulated power supplies.

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    \$\begingroup\$ I didn't downvote you (!), but I'll point out that you can most often safely replace a linear adapter with a switching one, but the reverse is not true, so the interchangeability is one-way. Have a +1. \$\endgroup\$ Commented Mar 14, 2015 at 2:16
  • \$\begingroup\$ @SpehroPefhany: Why can't you replace a switching power supply with a linear one? \$\endgroup\$
    – Dave Tweed
    Commented Mar 14, 2015 at 2:20
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    \$\begingroup\$ Because the switching ones are virtually all regulated- for example 5V@2A and the linear ones are almost always unregulated- so if the load is light (not all loads are steady) you could see a much higher voltage and the product could malfunction or fail. \$\endgroup\$ Commented Mar 14, 2015 at 2:23
  • \$\begingroup\$ Yeah, the other problem is that some switching regulators will introduce switching noise into poorly designed analogue circuits (like amplified speakers) so making the other migration direction also a possible problem. In this case I think both could work fine. \$\endgroup\$
    – KalleMP
    Commented Mar 14, 2015 at 7:16
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    \$\begingroup\$ @KalleMP: On the flip side, some speakers may filter out high-frequency noise from a switcher more effectively than they filter out 60Hz ripple. \$\endgroup\$
    – supercat
    Commented Jan 23, 2017 at 21:57

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