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I have a whole bunch of old power supplies from various electronics that's long gone. I cut off all the cables that I guess would go as "insulated cable", and then I tried getting copper wire out of the AC-DC converter transformers. Just taking apart the plastic casing took forever, then I realized I had no idea how to get the copper wire out of the transformers themselves. Has anyone tried this and succeeded? The idea would be to take apart it fast otherwise the relatively small amount of copper will not make the whole effort worthwhile. Thanks.

Some of the more obscure power supplies are worth selling or keeping as spares, but most are safe to scrap.

Usually power supply cables are classified as #1 insulated wire. Most of the time they're not plated, but it's always good to check.

The yards near me will take the power "bricks" - intact with plastic and all - as electric motor scrap (also called "copper breakage"), provided a significant portion of their weight is from the transformer. Some yards are pickier though and want all plastic and/or small circuit boards removed. Call ahead or bring a small sample before cashing in a full load of them, as like any other scrap material prices can very widely.

It's not worth the effort to bust open the plastic boxes if you don't have to. And separating the small windings from the steel is even more tedious. Always consider the cost of your time and electricity required.