Well volts x amps=watts you can go the other way as well.... Soo if you have a 100 watt device and you have a 12 volt supply then you would need a continious amp rating of 8.3 amps. Now because your radio is not driving your 100 watt device at any where near 100% because of the way your modulation works you can often get away with a little less since you only hit 100 watts at 100% modulation etc....
You clearly do not understand efficiency or how a radio drives an amp. P=V x I however that is just DC power into the amp. Power out is equal to P=V xI x eff. Most solidstate amps are about 50% efficient unless it is a class C crap box and then you might see 70%. Therefore a 100 watt amp would require 12 v x 16.66 amps x 50% for a total of 200 watts input for 100 watts output. the rest is heat. Hitting full output only at 100% modulation still means that you need the full current available during peaks.
I had a second generation RCI 2950 that had 2 x MRF455 transistor amp bolted onto the rear of it's chassis. I put it on a friends 32 amp power supply with amp meter. It varied between 11 amps and 15 amps depending on the amount of RF power I had selected.
Either the radio was not driving the finals to full output or the meter you were measuring current with was too slow to show peak current and was reading low just like trying to read pep power with an average reading meter which will always read low.
Linear power supply uses a heavy transformer made with high silicone steel and lots of copper wire. Depending on who makes it you can see various capacitors, rectifiers and Fe bead or toroidals before the output to the terminals. The less rectification the less noise. If it is AC to DC transformer you can just filter it with a cap and Fe choke.
An AC to DC transformer? No such device exists. A transformer is an AC device. Ac in on the primary and AC out of the secondary. Also not sure what you mean by less rectification. Rectification is the process of changing AC to DC. Nothing more and nothing less. Less rectification ? Is that like using a half wave rectifier instead of a full wave rectifier? A half wave requires a bigger capacitor to filter out the higher level and lower frequency of ripple.
If you look at old battery chargers they often used ac-ac transformer and then a germanium rectifer to turn it to DC and had no caps or Fe chokes on them.
They ALWAYS used an AC-AC transformer. there is no other kind. Transformers do not pass DC nor do they convert AC to DC
Linear AC-DC transformers are not very efficient, are expensive and heavy but produce a very clean power that is low ripple and usualy free of birdies. Expect a lot of heat so keep them where air can circulate!
Please stop calling them AC to DC transformers. I believe you are looking for the words "power supply". Yes linear supplies are heavy and bulky and less efficient than switching but they are easy to repair and will take more of a beating if something goes wrong. I prefer them for their clean output and serviceability.
Switching power supplies work in much the same way your alternator on your car works. Your alternator makes AC and it uses a bunch of diodes to take that high voltage AC and produce something that is very very similar to DC. They are noisy and dirty. That is why I will never take power directly from an alternators out put I always want it to either go through a lead acid battery (think electrolytic cap) or I put it through a filter sometimes both!
The alternator is noisy because of the voltage spikes that are developed from the brushes and slip rings. The output is a high frequency AC that is rectified to pulsating DC which is filtered by the battery. It is much higher than the nominal 12 volt and feeds a voltage regulator to maintain a nominal 13.2-14.4 volts depending on the rate of charge.The high pitched whine you sometimes hear is a result of that high frequency output. You are correct about never running anything directly from an alternator without a large filter, preferably a storage battery and even if that battery is bad it will provide filtering.
AS far as head room goes I like to have at least a 30% reserve based off of the continuous rating of the power supply if it is switching. If it is linear I will reduce that some.
Usually a good linear supply can be run pretty much right up to it's maximum ratings but switching supplies do indeed like to have a little headroom left. A linear supply generates most of the heat in the transformer and pass transistors on a heatsink whereas a switching supply, although they create less heat, tends to generate that heat in smaller components that need better cooling.
