Here's the questions you need to investigate before purchasing a supply:
1) Does the input voltage range match your available AC power?
Not a concern with a switching supply as many will operate from 90 to 250 volts and 50 to 60+ hz with no change in output.
2) Is the peak output current rating of the supply at least as great as the peak current consumed by the transceiver? More is better. Don't forget to add in the current for any accessories that you may want to run from the same supply.
This is over rated. I used a RS-20 for nearly 20 years heavily with 4 different rigs and it never had a problem properly feeding them. A 20 amp supply does not hit a brick wall at 20 amps. The 20 amp rating is for 50% duty cycle which is SSB is never reached unless digital for long transmissions at full power. Also none of the radios I checked actually drew full rated amperage. Usually the draw less. Manufacture rating is conservative because it is better to rate a rig at say 22 amps and have it draw 18 or 19 than rate it at 19 and have it draw more.
3) Is the supply linear or switching? Each has its advantages. Switching supplies are smaller and lighter for the same output rating but they can generate RFI (RF Interferrence to your receiver) if not well shielded and filtered. The closer your antenna is to the supply, the more of a concern this will be. Switching supplies usually contain a fan which can create acoustic noise in the shack. Linear supplies are larger and heavier but are not likely to generate any RFI. My personal preference is for a linear supply if I don't have a need to transport it.
I have never had a problem with this and my house is full of switching supplies in computers, TV's power adapters for laptops and so no. The fan in my Astron SS30 does not run often and is not very loud and besides I never place supply on desk anyway as I place them under desk on floor but elevated some for proper ventilation. Linear supply cost more to operate and are far more in efficient (power in vs power out)
4) Make sure that the supply has "over-voltage protection". If it doesn't and one of pass transistors shorts then a linear supply is likely to apply 24VDC or more to your transceiver - not good!
You need to hope "crow bar" works on a linear supply or it can fry rig if it fails. With a switching supply output goes to zero if unit fails.