In the first half of the 20th century, there were a lot of radio installations, used to relay messages for the military and others. They used big banks of lead-acid batteries, and I'm sure the most cost-effective way to charge them was with DC generators. I suppose in more settled areas with AC power they used a few rectifiers, but I assume generators were the preferred option for a long time.
Remember "the first half of the 20th Century " takes you right up to 1950.
Things changed with breakneck speed in that first half century.
Certainly, by the 1930s, the large radio installations in Australia used AC power, either off the grid, or locally generated.
Tube transmitters of any reasonable power output require high voltage anode & often screen grid voltages.
The easiest way to obtain these was with HT transformers & mercury vapour rectifiers.
There were Broadcast Stations which used the DC mains, but they were often limited in power output, or did use motor inverters.
Broadcast and/or Comms Transmitting sites were very costly to put together, & needed Emergency Power Plant.
An AC EPP is less costly than a DC one, both in construction & maintenance. (slip rings & their associated brushes don't wear as rapidly as their commutator counterparts).
Some Radio Broadcast sites ran completely on their own locally generated AC, as there were no Mains supplies either AC or DC in the area.
6WA, in Wagin Western Australia, is a case in point, where the Radio Techs & Diesel Mechanics lived in a little "village" onsite.
The Diesels required a method of starting, which could be compressed air, or batteries.
It was often the latter.
In any case, even if the larger battery banks required for electrical starting were not needed, it was common to reticulate 24v DC throughout the building to handle those functions which needed to be maintained during a power break.
This was normally derived from the AC mains during normal operation, automatically switching to battery during power loss.
As copper-oxide, selenium, & Tungar rectifiers were inefficient, the chargers had large stepdown transformers, very big rectifiers, & hence the whole assembly was big.
There tends to be an assumption that, as new technology was developed, the "old hat" stuff was dumped, & replaced with the "latest & greatest".
After around the "Thirties" this was far from the case, as very few organisations were eager for the capital outlay to replace perfectly capable, reliable equipment, to gain a few percent of efficiency.
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