Travis Jordan wrote:

I have a very well-built OEM PC PSU that has two thermistors, one for
each AC line. One thermistor is fairly large, the other only half its
diameter. What's the purpose of using two different sizes like this?

Good question. Are you sure that they both are thermistors and that one
isn't a fuse link or RF filter?

Here's a photo:

http://static.flickr.com/42/75028029_3a711a4666.jpg

I'm pretty sure that the two black things are thermistors because
they're labelled NTC1 and NTC2 The RF filter is in back of them in the
photo.