'UK adapter in a US plug' question...

considering electrical stuff in US operates at 110/120V and UK stuff operates at 220/240V, would it be reasonable to suggest i could use a low powered lamp that has a UK 3 pin transformer (output = 5V 0.5A) with just a plug adapter for the US?
I dont need to use a 'step up' transformer?

adapter is AC-DC with 3 pin UK plug on the end.

Assuming you mean power supply, rather than transformer, it depends. Most older linear power supplies can only cope with a very limited input voltage and frequency range, whereas new switching power supplies can cope with a very wide range of input voltages and frequencies.

Have a look, there should be a sticker or label which shows the allowable input voltage range. A switching PSU may be something like 100-240v, which means it'll pretty much work anywhere in the world. A linear PSU will likely be something like 220-240v, in which case it won't.

Does the 3-pin transformer for the lamp have the Input voltage range printed somewhere on it?

Eg. INPUT 100-240V-50-60Hz 0.5A

UK adapter label states:

input: 100-240V ~50/60Hz
output: 5.0V 0.5A

and its not linear, its a switch mode power supply.

Aye, that'll work then!

awesomes.
i do know that larger items such as washing machines etc shouldnt be plugged in via a plug adapter (UK to US) as the lower voltage doesnt provide enough power to motors etc...but why you would take a washing machine all the way over to the states is beyond me.....

I've known people who've brought washing machines and fridges back from the US...would have been before mahoosive fridge freezers were popular over here (late 80's early 90's).