So @johns_az looked at the schematic I was going to use for the LM338T power regulator and immediately said, "There's no fuse."  And being the awesome guy and amazing schematic drawer he is, he drew this:

Bigger version here: http://www.tymkrs.com/forum/viewtopic.php?id=27

Anyway. So I'm to the point where I'm looking at fuses.  And John suggested I get this one from Radio Shack: http://www.radioshack.com/product/index.jsp?productId=2103770

It's rated for 250VAC 1.0A.  That's cool, but I found that we had some fuses that we got from some Electronic Goldmine random box and they're rated at 250VAC 2.0A.  So I wanted to see if these would work just as well.

Well the main thing then is to figure out whether the transformer can handle 2 amps of current (which to me sounds like a tiny amount).  So I asked around and tried looking for a datasheet which gave me this:

Now this was where I got /really/ confused.  Because you almost never not find a datasheet for some electrical part.  So okay, to the twitter folks!

@atdiy: I'm looking for the max current this transformer can handle.  http://parts.digikey.com/1/parts/999535-transformer-115vac-18vct-1-5a-166k18.html

@eevblog: Trick Q? It's rated at 27VA.

@IdeaPDish: Click on the link in your tweet. Read the box next to max. Lookup 'VA' in Wikipedia.

So I looked up volt-amps and it says: "A volt-ampere (VA) is the unit used for the apparent power in an electrical circuit, equal to the product of root-mean-square (RMS) voltage and RMS current."

Fine no problem, I have (secondary) RMS voltage and RMS current.  Multiply those to get VA:

VA = RMS(volt) * RMS(amp) = 18*1.5 = 27VA

So then. The root mean square amperage IS the max amperage?  And this would mean that the MAXIMUM input current is the output current of the transformer? 

Anyway, this would seem to say that the fuses we have around the house (250vac 2amp) would allow too much current to pass through for our 1.5amp transformer.