The market for security equipment makes it easier to put together a power distribution cable based upon 5.5×2.1mm plugs.
Start with a Y cable that has a female input and 4 male output plugs (all 5.5×2.1mm).
Take a 3 foot (add zip wire as needed) 5.5×2.1mm male pigtail, and carefully mark negative and positive terminals. After the whole assembly is done, verify with a voltmeter on the ohms scale, or with a battery and test light, that there is continuity between the wire that you have marked minus, or negative, and the outer sleeve on all the male plugs (failure to do this correctly can wreck your devices).
(Just because I didn’t want surprises in the field, and we are using overseas parts, I tested the continuity of the positive lead, and the inner pins of all the plugs).
$6.99 — Barrel-Converter-2-1mm-5-5mm-2-5mm (purchase this item and avoid needing next item, and the soldering operation).
$5.86 — 5.5mm x 2.5mm DC Power Plugs Male Barrel Connectors Black 6Pcs — be sure to wrap the metal ears around the black plastic securely as strain relief for the plug — see the above picture showing this.
$9.99 — VideoSecu 10 Pieces 36 Inch CCTV Security Camera DC Male Power Plug Pigtail Cables PC01T C58 — 10 pieces is more than we need, but they are useful to have–maybe you can buy fewer–things keep changing on Amazon.