So, I might as well give a hand spelling things out.
Loads on the power supply:
Heated bed: 1-1.1 ohms. Total current draw, 22-24A.
Motors: ~.8A each, 3.2A total (assuming single extrusion, and not lowering current from the defaults)
Hotend: ~2A per heater cartridge. Do not attempt to use the stock resistors, or a 12V cartridge, as that will end up drawing ~160W briefly, before the leads to it or the fuse gives up the ghost under 6A of load.
Cooling fans: these should draw a small load. Much less than 1A total unless you have some real in-efficient enourmous fans (For example a 200MM fan has a .3A draw in many cases, and is total overkill for part or hotend cooling).
Overall, I would not recommend going 24V totally with less than a 35A power supply, and more likely a 40A one I recommend either a Meanwell SE-1000-24 for it's cost (40$ cheaper than the RSP model at 177$), or the RSP-1000-24 at 215$ for it not having large blade terminals that carry the 24V current, instead having more normal screw terminals. Both of these supplies are 40A+, and feature some nice things like a remote on-off, and voltage sensing. That makes it a lot easier and saner to wire them into a printer without having to worry too much.
But you will have to change the heated bed wiring, add a solid state relay to control that current, and change over all the fans you use and the heater cartridge or resistors in the hotend. If you have any LED's running off the power supply, such as chamber lights or an illuminated switch, those need to be checked for 24V compatibility (Probably not), and either have a resistor added to reduce the voltage drop, have two sets wired in series to accomplish the same thing, or be changed out.
You're looking at a price tag that's probably around 300$ to do everything, plus shipping from at least 3 places (Hotend or heater cartridge vendor, possibly amazon, Mouser or similar for the power supplies, and Auber Instruments for the SSR). I would also very much recomend that if such an upgrade is carried out, silicone jacketed wire is used for the heated bed connection (10 gauge is what I used, but it doesn't fit particularly well the way I have it wired. If you have a higher bed spacing or are more willing to drill through the plate, it will work better. I'm just going to use FSR's which will lift the bed anyways and be happy with that)
You can also take the RC hobbyist route, and isolate DC grounds in a power supply, then wire it in series with another one, or buy it off the shelf. But while these are cheaper ($75 + shipping), they add to the odds of something going wrong, and unlike Meanwell supplies, it's hard to get anyone to stand behind them if they blow up. It's for the same reason I don't recommend you buy an Ebay or Amazon power supply for cheap (besides the obvious issues of many of those listings not being at all clear and others being clear lies, and there being few units at those wattages)
Now, some stuff you really don't need to do, but I'm going to recommend you do anyways as you'll be tearing up a large chunk of the wiring to do this, and making a LOT of power available. First, I'm going to recommend you get a nice hefty bus bar which supports individual fusing such as
this, and then have a 30A fuse for the heated bed, going to the SSR, and 5A fuses in the other 3 going to the Rambo supplies (perhaps a 3A for the one going to the heated bed terminal on the Rambo as it's only switching a relay now, and replace the 15A one on the board too). Run 8 gauge wire from the power supply to the bus, and 10 to the heated bed. Beyond that, 14G should be more than enough for the other branches and is easy to work with. If you don't already have a decent soldering station with temperature control, get one. Soldering the wire to the heated bed works a lot better with more than the 25-40W the simple plug it into the wall home depot specials can muster. Nice benefit for you is that if you use 5A fuses in the distribution block and 10A on the Rambo, then if you blow anything you can hit up a wallmart or any other shop for new ones rather than ordering them. I will also recommend using a terminal block in the top to handle power going to the hotend and fans. It makes it much easier to work with, and depending on the style you can either get them rather cheaply (I paid less than 5$ for a 14 position 20A one), or with lots and lots of connections and other nice features like being able to toss a fused blade in or having individual screw for up to 4 12G wires if you want to spring for some DIN rail terminal blocks
Feel free to ask any questions you (or anyone else has). If I don't have an answer, I can run it by the industrial electronics folks fairly quickly.
