My 2 cents...
I think these guys are trying to swindle you. Although, they could just be very dumb as well.
What brand of memory did they have in the system previously? Corsair has a lifetime replacement warrenty, as do most other name brand manufacturers (Mushkin, Patriot, Viking). Demand to know the manufacturer and part number, and demand to know if they have attempted to RMA the product.
If a failed power supply damaged their memory, I would suspect that they had a faulty mainboard to begin with. Power supplies have fuses, and mainboards have regulators. Spikes in the power supply shouldn't just nuke memory, it should nuke every other component that gets its power from that rail.
I call BS.
Of course, I've been in this boat before. When I was much younger, I had an Amiga 3000/030-16 desktop computer, and I borrowed my friend's 68040-25 processor daughterboard. Damn thing overheated and blew my whole system out. His board still worked, but my mainboard was toast.
I sucked it up and took the loss. It wasn't my friend's fault that my computer couldn't take it. Sometimes these things happen.
The guy who let you use his system should have been aware that you were putting stuff into his server. If it blows up because your components overloaded his stuff, he should suck it up and chalk one up to learning not to buy the cheapest gear he can get.
Garbage in, garbage out.