For wiring power to your Ring Video Doorbell Plus (that does not have an existing wired doorbell) you are correct that you’ll need 8-24 Volts AC, 40 Volt Amps (watt) max, and 50/60Hz. So, both of the two Amazon Transformer choices that you listed are both fine to use. It’s basically your personal choice as to which one to purchase. Either transformer would be sufficient to provide the necessary power to “Trickle-charge” one or two doorbells. Although the lower power transformer should be sufficient, if you also later decide to add an indoor wall-mounted compatible House-chime, I kind of agree that the more powerful 24V 40VA might be the better choice transformer (especially since their prices are almost the same).
Whichever transformer you decide to purchase, remember that these do produce heat and get warm, so do not enclose the transformer in a wall where there is insufficient ability to be exposed to cooling air. That’s why you typically find the transformer mounted exposed in the house’s crawl space, basement, or even in a closet if well-exposed.
Unlike some earlier doorbell models, to connect your “Ring Video Doorbell 3 Plus” directly to a transformer, you will not need any wire-wound resistor nor a diode. Just connect the wires directly:
If you change your mind and decide to additional install a house wall-mounted chime, ensure it is compatible:
You will also need to change the default setting on your Ring App for the “In Home Chime settings/Advance settings” from “None” to “Mechanical” or “Digital” chime (the default setting is “None” because Ring has no idea which type of house-chime you might have). If you leave the default “None” setting, your house-chime will remain silent.
Also as a 'heads up", the Video Doorbell 3 and 3 Plus have an unique charging schedule. A hardwired Ring Video Doorbell does not actually use the power from the wire to run its operations. It relies on the battery for that. The trickle charge the Ring Video Doorbell 3 Plus gets from being hardwired or the solar charger is solely used to charge the battery. In order to maximize the lifetime of the battery, the new Ring Video Doorbell 3 and 3 Plus waits for the battery to hit below 90% before using the wired power to recharge the battery So, when the battery power decreases, don’t think the hardwire isn’t initially working since it needs to fall below 90%. And the doorbell’s battery level may still continue to fall if it is draining fast from multiple motion-triggered events. Once the event rate decrease, then the slow “trickle-charge” should catch up (from note at the bottom of this link):
I hope you find this information helpful.