So I went to visit my mother and neither of the LD players at the house are powering on (D605 is my mother's and the D505 is my brother's.) Tried using three different power cords, but no dice on any of them. I might have just gotten some really bad luck with AC cords (I am going to go and buy another AC cord tomorrow just to be safe), but I'm thinking I have some bad power supplies.

Short of sending this out to have these replaced, I do have some non-working players--a DVL-700 and a DVL-919. I don't suppose those power supplies would be interchangeable with either of the aforementioned players?

And would it be very difficult to DIY the replacement?

if you've done this type of soldering etc before i don't think it should be hard.
but if it's more than that there will be issues.

Take the top off and see if the fuse is blown, guessing it is. Just cut out the cheap arc suppressor that is shorted probably D106 by the AC input connection and replace the fuse. Just buy an outlet strip with power surge protection.