USB was created by computer bods, and was immediately grabbed by all and sundry to power everything. Designed to give enough power to allow a good data feed, it is rated at 500mA.
Most dash fitted USB ports will be the standard 500mA. Some manufacturers are giving more power, btu these will usually be marked with their output, so if unmarked, assume 500mA. Not enough to maintain a smartphone using nav, let alone charge it.
When cigar lighters were invented, there was quickly a European standard, which Fiat still doggedly use. The Japanese, didn't conform, and standardised theirs slightly smaller diameter. Most manufacturers now use the smaller size.
Accesory plugs have to be able to fit into the smaller socket, and have spring clips that hopefully expand enough to grip the larger holes. Sadly, it is rare to find one that fits snugly. Even tight ones will wobble, especially with a cable hanging off it, and will occasionally disconnect.