This should be fine with such low power appliances. Just make sure the extension cables are decent quality and that the plugs are fully inserted.
Obviously make sure they don't pose a trip hazard.
Welcome to the forum!
What's your electrical background? Presumably you aren't expecting to go from zero to working in people's homes in 14 days.
Worth checking out some of the other threads on here with a similar theme. Not of good info and advice to be picked up.
If the gauge isn't intended for DC operation then that is probably your problem.
Don't use the left hand socket, that is for current only, and will effectively short circuit anything you connect between it and the centre socket.
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