What do folks do with old SMPSs?

If it's a higher-end iFi SMPS like the iPower II or iPower X, keep it and sell it. It gets good reviews and holds its value.

Put them in a box and carry them with you for the rest of your life no matter where you move to.  That's just what I do though.  

Our regional waste facility takes them, presumably the copper gets recycled. Inquire locally to see if you have a similar program.

@erik_squires Yikes. That's me. I'm a gonna throw them all out tomorrow. Scores of 'em. Thanks.

@noromance That’s meet too, lol. Just filled up a garbage bag with dozens as well. It felt liberating!!