Many different power supplies are available to operate the 13.8 volt devices in your radio shack. Years ago most HF transceivers used 18-20 amps at 100 watts output. Now, some newer transceivers use up to 23 amps at full output. Most 2 meter or dual band 2m/70cm transceivers use about 2 amps on receive. Some of you may have seperate 2 meter & 440mHz transceivers so you would use about 4 amps in receive. Other accessories such as tuners or meters have lights, but draw very low current. Incandescent lamps can use about 300ma, LEDs are very low current at about 20ma. Twenty (20) amp intermediate rated power supplies may fall short on current and fall out of regulation with newer HF transceivers plus other items connected to the power supply. However, I did draw 22 amps peak from an Astron RS-20A without losing regulation on low duty cycle SSB transmit. The RS-20A linear type power supply costs about $120. It uses two 2N3771 pass transistors where as the RS-35A uses four 2N3771 transistors. 11 amps thru each 2N3771 is pushing it in the RS-20A vs 5.5 amps each in the RS-35. Do note the RS-20A had never failed after 20 years use. Another consideration is reliability & type of power supply being linear type or switching type. A linear power supply simply reduces a higher than 13.8 volt DC source such as varying 17 to 22 volts to a steady 13.8 volts DC. Although losses of the voltage difference are dissipated as heat, linear type provide the cleanest DC output with most under 5 millivolts AC ripple on the 13.8 volt DC output. Switching type power supplies convert the 12o volts 60Hz input to high frequency around 400Hz to 1kHz. High frequency uses a much smaller iron core transformer vs 60Hz for same power output. The variable input voltage that is adjusted to the transformer output voltage after rectification and filtering is set at 13.8 volts DC. Much less losses in heat vs linear power supplies make the switching type power supply more efficient. Switching power supplies require RFI filtering to reduce noise on the HF bands. Poor designs will interfere with your receiver reception. I think now a days most switching power supplies are quiet enough in operation. The most reliable power supplies I know of is Astron. Aston manufactures a RS35A linear type and a SS-30 switching type power supplies. I did not consider 20 amp rated power supplies due to I do use more than 20 amps in my shack. I do not care for meters myself as both Astron power supplies regulate the voltage to 13.8 volts DC and if the regulation fails (higher than 13.8 volts DC), the power supply will shutdown. I am also not concerned with amperage draw. If you want meters, expect to pay about $20 more. The Astron SS-30 costs about $99 everywhere and the Astron RS-35A is from a low of $179 at HRO up to $219. I bought the Astron RS-35A due to the ultra simple circuit design is less likely to fail vs a switcher and the ultra clean DC output of the linear type power supply was desired. So, I highly recommend the Astron RS-35A and is much more heavy duty vs the linear type Astron RS-20A. Astron has been manufacturing power supplies for over 40 years.