The generic Dell looking one can never be used for mining.
I had similar PSUs as these in my GPU mining days. I just sold them on Craigslist for like $20-30.
You're right, to be honest, also in term of efficiency, but people come here to buy or sell computer components too, so maybe someone on a tight budget to build a PC would grab one. In that case it would not be a bad idea at all.
Its still a little too much.
You can get that that Thermaletake for $16 from Amazon if you are in the USA.
http://www.newegg.com/Product/Product.aspx?Item=N82E16817153165&cm_re=Thermaltake_TR2_500W-_-17-153-165-_-Product
The Corsair you can buy brand new for $40.
I had both those PSUs and I think I gave one away for free with a GPU and another I sold for $20.
Good for you.