12v power supply old vs new

Got my Compact 4 mixer on ebay, came with a beat up old type heavy power supply. After a while the output wire broke at the case. Bought a similar used adapter on ebay and also a new $12 lightweight adapter from amazon. Tried the new one. Didn't like. The used adapter lasted a few years until 2 weeks ago when it's output cable also broke at the case. On a project so started using the cheapie. Noticed the mixer was getting warm (maybe not enough output amps ?) after a couple hours of use with phantom 48v to the mic which never happened with the heavy adapters. Specs on the labels for old and new types are same.

Found a new $45 (!) heavy adapter on amazon, spec and type per manual for compact 4. Running nice and cool again. Googled old vs new, some say toss the old heavy type. Maybe that's not such a great idea.

Not all switching power supplies are created equal.
I‘ve had the same experience once with a 16 channelAD/DA converter, also powered by a heavy „old style“ PSU. It got warm, but nothing extraordinary.
Since the transformer would draw significant power when idle, I tried an IBM ThinkPad PSU (almost identical specs) because I knew it would switch itself off if the notebook was powered down. (the PSU wasn‘t warm in that case).
This replacement worked great.

One day a fellow with the same converter complained about excessive heat, if powered by a cheapo no-name supply (with matching specs of course).
His old heavy block had died, so he got the next best replacement.
I replicated his setup and indeed... the converter got so hot, one might have fried eggs on it.

Essentially the power regulation inside the converter worked (kind of) against the switching PSU. No idea about the technical details of the 2 PSUs, but the power regulation inside that converter is quite unusual... I wouldn‘t have expected to ever read about a similar case.

My $12 one was also no-name. It's prongs didn't fit my extension cords well. A little loose. The label says input 100-240v AC, my new and used heavy ones say 120v. Don't know if that matters. Also I read that the switching adapters can be noisy when used with audio equipment. I didn't notice any noise though.

Most cheap switching PSUs have 2 pin main connectors, intended to run „un-grounded“.
Some of these emit constant noise, sometimes the noise depends on the direction it‘s plugged in, but that may vary with (individual) power installation.
If you have (say) 4 such PSUs, there are 16 possible combinations to plug them in.
(one can only find the best combination by trial&error)

Usually switching PSUs with a 3 pin connector have a better quality and are more expensive, but there‘s no simple rule of thumb to generally avoid ground problems.