Hi
why you think 80 C is a high temperature for a power supply circuit
when a approximately 20 watt none switching power supply works it's temperature rises about 150 c !

you want a 24 V DC 50 watt power supply
and if you don't want to waste your money you must make it by urself
now i'll guide you to make a power supply under above conditions:

first you need a step down transformer (132 VRMS to approximately 24 VRMS) note: 24 VRMS not 24 v peak!

then you need four atleast 2 ampers  diods like 1N4007
(rectifier bridge)
and a 30 V 2200 uF capacitor

after that you need a LM317 variable voltage regulator
(with a heat sink) to adjust output voltage to 24 v
it works only with 2 resistors
you can see it's data sheet at www.national.com
after LM317 it's better to use a 25 v 10uf capacitor for a none ripple output.
and for obtaining 50 watt power you need a power transistor like 2N3055 it works even in hell's temperature!
lol
note you must use a big heat sink with 2N3055 because without a powerfull heatsink it's tempreture will rise up to 200 c!
wow
after all if you can it's recommanded to use a fan beside your circuit.

now your power supply is ready and it's very very low cost

just a supplement to biomdicalengs suggestions

go with the tx and diodes and build a coarse supply close to the figure your looking at now look at some of the 555 circuits in the national semis book or something like the "555 cookbook". You should be able to dig something out of that.

  If that doesn't amuse you try grabing a cheap op amp (say TL071 app 50c) and a cmos gate say a nand and use this to build a simple oscillator about 200 - 300 hz feed the triangle wave from the oscilator cct to the invert( I think - beware virt. earth) input of the amp and then set a reference voltage with a zener or a resistance divider on the input dc. If you set a very high gain this will give a sq wave to drive say a BD139 (cheap as!)You will get a pwm output so stuff this into a suitable cap and you're away
 This a the moment is my favorite grab box for expirements and utility work. Note because we are switching the BD 139 the power dissapatted is bugger all.

Any way let us know how you get on.
Regards Don

Thanks for the responses so far, but before I get similar advice from any more people, I'd better clarify the situation.  This power supply I'm looking for is to be incorporated into a commercial product, so it needs to be UL certified.  The time and added expense of prototyping, testing, UL certifying and manufacturing my own power supply is prohibitive.  That's why I'm looking for an off the shelf supply.

In response to biomedicalEng, if the temperature of some switching supplies rise to 150°C as you say, then why are all the commercial ones I've investigated only rated to 50°C?

pjm7
  OH , it was a good idea while it lasted. I don't got no good ideas but let us know if you have a win

Regrds
Don

Suggestion: Try military grade or government off the shelf product, which may eventually be custom made, e.g.
http://www.atcpower.com/military.htm
http://www.abbottelectronics.com/sales/nw25S.htm
etc. for more info

Suggestion: Visit
http://www.abbottelectronics.com/sales/nw50d.htm
for 50W 24VDC 90°C ac - dc power supply