Yeah, C4757p, an LED strapped across a 24V 40A power supply oughta be bright enough!
For a short while, anyway... BLINDING FLASH=High Current Power Supply ON!
Sam, this is an interesting project, but i am inclided to agree with others about the dangers of trying to build a one-size-fits-all solution. A supply capable of delivereing tens of amps won't be easily and safely controllable down at hundreds of milliamps, I'd suggest
Do you need control of the current, voltage, or both? If you are talking about significant power, here, can you not get away with a Swithed Mode power supply? But an SMPS is not the best place to start a complex high power project, if you don't have previous experience, I'd respectfully suggest. I might look for a prebuilt controller, and then build a case, metering, sockets, etc., to suit my project.
And be careful! Just because it's 12/24V, doesn't mean it's "safe", if there are tens of amps behind it. I once saw a telecoms engineer weld himslef to a piece of equipment with exposed 48V power supply bus bars, with his metal watch strap... which he shouldn't have been wearing, of course.