Standard Powered Female DC Connector
DC outlet standards

There are various standards for low-voltage DC distribution, often de facto, or of narrow application.


5 V:


USB connectors, generally either Type A sockets or several possible plugs on 'captive' cables from the power supply (Mini-B, Micro-B, C).

In principle, each device must negotiate for its current draw, or at least check that the supply is a USB BC 1.2 device, i.e. one with the data pins shorted, which is a promise to be capable of supplying 2 A. In practice, this is often ignored.

12–13.8 V:


"Cigarette lighter sockets" (or renamed "accessory/auxiliary sockets") in cars. Available in almost every car, so DC powered devices may have official "auto adapters" available for them, but they're very bulky.
Anderson Powerpole, commonly used in amateur radio systems.

48 V:


Power over Ethernet. Commonly used for devices which require power and wired communications, such as WiFi access points and security cameras.
Phantom power for professional-style microphones; like PoE this is carried over the signal cable.

(Consumer PC/smartphone microphones use 3-5 V delivered in a different fashion known as "plug-in power".)

Variable/other:


USB Power Delivery allows negotiating for higher voltages up to 20 V over USB connectors, allowing more efficient transmission with the same cables and sockets.
Common barrel connectors: I've seen a lot of devices which take either 12 V or 15-20 V (the latter typically having a buck converter immediately after the input) through a barrel connector of 5.5 mm o.d. and either 2.5 mm i.d. or 2.1 m i.d. These two sizes of barrel connector are very common and you can readily purchase Y-cables, "octopus" multi-plug power supplies,  and all sorts of adapters for either size.

Unfortunately, the choice between 2.5 and 2.1 mm center pins seems to be done essentially at random, though perhaps with a slight tendency of 2.1 mm for 12 V and 2.5 mm for 15 V. I can't recommend this as a standard to build a large system on, but it can be useful info for adapting a device or for small systems. I have not seen any "outlet" (as in, male connector fixed to a panel rather than a cable) for this type of connector, though surely some have done it.
Since someone mentioned it and I'm trying to be comprehensive, IEEE 1823-2015 Universal Power Adapter for Mobile Devices. I haven't heard of any implementations of this standard.



DC bus issues

There are several things you must consider for practical use of a DC bus.


You must choose a voltage and be prepared to use converters from that voltage to the required input voltage for each device. The higher the voltage, the more efficient the bus will be (or equivalently you can pay for more copper in the bus cable).
Because you are using a power supply capable of high current, you must consider short-circuit failures. This means making sure that the bus is capable of carrying the maximum current safely, and either protecting each outlet with a fuse or other overcurrent device sized for that outlet, or oversizing all their wiring and connectors. You also have the risk of damaging individual devices in cases where their original power supply would have simply shut down for overcurrent protection.
Your system may result in increased electrical interference between devices, because noise can be coupled through the shared power supply (notice that the supply voltage will fluctuate as the load changes, if nothing else due to wiring resistance). You probably only care if you have analog audio devices on your bus, but extreme cases can also e.g. interfere with touchscreens.
Common "wall-warts" with two-pin plugs are isolated. This means that neither the positive nor negative output is tied to the earth/ground of the mains/line power. High-current DC supplies almost always are designed to connect the negative side to earth. Often, this is fine; it may even remove 60 Hz "hum" in your system, but it can also increase noise as discussed above. But worse, some devices may have been designed with the assumption that the supply is isolated and, if they have connections to other devices connected to the same power supply, connect two circuit sections that were assumed to be isolated, either resulting in extreme noise and malfunction, or even damage (e.g. if for some reason a signal ground is tied to the positive supply rail, which works fine as long as the supply is isolated).

If the devices you are considering are documented to accept a generic DC power supply (as opposed to “use only with the supplied power adapter”, then this should not be a problem; outside of that, proceed at your own risk (and maybe examine and probe the circuit first, such as by checking for continuity between the power input terminals and any connectors' shields/signal grounds).


Choosing a DC standard

As concrete recommendations if you still wish to pursue this: 


If you want to be most in line with consumer electronics standards, you should use USB for your power distribution. You can even buy multi-port USB power supplies as a commercial item. However, this means that each individual device needs to be either able to run off a small amount of 5 V or support USB power negotiation. You can retrofit negotiation with modules like the PD Buddy Sink or EZ-PD.
If you wish to stick to easy hobbyist builds with no additional electronics, look into using 12-14 V and Anderson Powerpole connectors as used in amateur radio and related hobbies. Stores such as Powerwerx will sell you a wide selection of parts for this style of system, including such things as wire, connectors, battery management for a UPS system, 5 V USB converters, fused distribution boards, adapters to "lighter socket" for plugging in devices with car power adapters, etc.
Choose Power over Ethernet if it makes sense to include networking, you have devices that support PoE, or have long cable runs (because it uses the highest voltage). A "PoE splitter" can be used to break out the DC supply for retrofitting devices.