Does anyone know
(a) the relative sizes of these different power supply size formats
(b) which reasonably available cases use TFX or SFX
(c) what are some decent models of PSU that come in the TFX or SFX size?

ATX: 150mm X 86MM cutout, original length 140mm, though most high power PSUs are 160mm (Enermax Gold, Enermax Platin<=600W, Seasonic X-series), some even longer: 190mm for Seasonic Platinum, Enermax Platinum >600W. There was an older high power (1200W+) Enhance design with a lenght of 220mm + removable cables.
TFX: 70mm X 85mm cutout, length 175mm standard, maybe up to 190mm
SFX: 100mm x64mm cutout (some have fans that protrude out->100mm X 77mm inside the case), length 125mm standard, Seasonic 350W 130mm.

Thanks Boost.

Does anyone know of any good cases that use TFX or SFX PSUs?

TFX:
Silverstone had some good desktop cases, LC02, LC04 and LC11, all EOL I think.
Chenbro Slim mATX cases are high quality and have an optional Seasonic PSU, though not the latest gold certified models.
Chieftek ITX mini Towers (1) (2), look in the galleries, someone posted pics of a build with one of those there.
Lian Li's mini ITX Desktops Q-09 and the upcoming Q09FN.
InWin BP series small towers and BQ series tiny ITX towers.
Yeong Yang mATX slim towers.
Mini-ITX.com has the Morex Cubid 3388, Jou Jye NU-528i-B and Jye NU-568i-B
SFX:
Silverstone Sugo SG05, SG06... , whatever front panel variations they have.
Thermaltake Element Q, very low clearance for CPU cooler. TT Luxa2 LM100, expensive.
Fractal Design Array, spcr review.
As you can see, compared to the number of bigger cases I could rattle of off the top of my head, there aren't that many.

Some of those are Flex-ATX power supplies, which are quite different from TFX.

Examples show:
Flex-ATX - 6" x 3.25" x 1.5"
TFX - 7"x3.4"x2.5"

http://www.directron.com/matxps.html

That's a big height difference when squeezing them in on their sides into the 'mini desktop' cases. There is a good review of a new 250W 'flex' form Seasonic here - http://www.xbitlabs.com/articles/cases/ ... html#sect0 . Perhaps it would be a good alternative to fit in all those low-profile cases.

And others take a micro-atx PS, which is different again: 146mm x 126mm x 74mm (5 3/4" x 5" x 3") with the fan sitting on top. The new Lian-Li Q09FN appears to take a micro-ATX form.

There are, at least 4, very different, non full size ATX, forms. It seems to me that many of the case specs don't tell you which 'small' PS they actually take!

Small 1U PSUs are sometimes refered to as flex, too. They are 40.5mm X 80mm X 150mm.
Regular 1U PSUs are 40.5mm X 100mm X 240mm-280mm.
Flex = flexible = manufactures use it however they want.
TFX and SFX are well defined.