Excuse this for being slightly off topic but it could apply to a
vintage or any car?

Some of the 12 volt to 120 volt AC converters now available at quite
reasonable prices can have a capacity of 175 watts or more. Some are
advertised as "Just plug in to your cigarette lighter".

Even at an efficiency of, say, 90% the DC input will have to be
(175/0.90)/ 12 = at least 16 amps! That's equivalent to approx. four
old style headlamps all on at once? I think I've seen a 25 wat model
that would take 23+ amps.

Recalling some difficulties with cigarette lighter sockets where
underdash wiring either caught fire or the socket itself got extremely
hot is this perceived as a problem?

Better, I guess, to use a pair of clips onto the battery itself and/or
use a separate fused circuit.

TIA welcome opinions.