What Do You Call a Store that Sells Obsolete Equipment?

I think of the sort of place you could buy a power cord for a flip-phone ... and the word that comes to mind is 'radio shack'; not because of the company "Radio Shack"--which sells the same up-to-date equipment as anywhere else--but the old-time definition---a 'shack' where they would put together whatever old equipment they could find to get the job done.

"Radio Shack" sound good for 'modern use of obsolete equipment'?

Surplus shop or store. Electronic surplus would be more specific.

Started as Army Surplus but doesn't need to be.

The commonly used term is junk shop (OL&G).

"a shop selling secondhand goods or inexpensive antiques"

You can add "vintage electronics" to convey it sells a lot of obsolete electrical equipment.

A thrift shop is a generic term for a store that sells used goods.

Definition of thrift shop : a shop that sells secondhand articles and especially clothes and is often run for charitable purposes

https://www.merriam-webster.com/dictionary/thrift%20shop

Most thrift shops specialize in clothing, furniture, household goods (kitchenware and the like), where the item sought is not specific. A specific item is more likely to be found on line, where a dealer may or may not have a particular item.