For me, a slam dunk for worst tech purchase would have to be two(!) JVC S-VHS VCRs! OK, I used to sell JVC, was able to get it @ 1/2 price, bought a couple of pieces on employee purchase terms. Their stuff never seemed to meet spec, do what they claimed it would, or even last very long. I wound up selling every piece I bought in a month or so.
That said, I don't know why I though it would be different walking off the street as a "civilian" and buying these two turds. One broke in a couple of months. The other I simply stopped using, and went back to my Toshiba VCRs.
In my own defense I'd like to point out that DVD recorders, (free standing) were about a $1000,00 at the time.
My "second worst tech purchase", would be long and storied list, which would probably do me irreparable emotional harm by recanting it to you.