Unless of course the machine is not wired properly inside and there are external metal components that are currently inadvertently connected to neutral on the inside. Since this most likely won’t work with any standard GFCI system either I’d say it’s a somewhat risky proposition.
Well, if that’s the case, it will go “bang!” and trip the breaker. If there is no hot-to-case leakage, there is no reason it should trip a GFCI.
FWIW, I have a friend who’s quite proud of his 230v electric kettle. He obtained this in England, put a US-style 230v plug on it, and has been happily using it for about 5 years (it boils water in a commendably short time).
Having had first-hand experience with things made overseas, I think I’d stick with the transformer idea. 
Man, just use a step down converter. I actually linked to one in my earlier post. If you need, you can use a plug adapter, but most step down converters have a universal socket that can take old style British, European, and American plugs.
Minor nit: You need a step up converter, not a step down converter, since you need to step the voltage up to a higher value for use by the espresso machine. The unit you linked to earlier can be used as either a step up or a step down unit, it just depends on which way you plug it in.
If you use a transformer like this, make sure it can handle the current. The unit madmonk28 linked to is rated at 3000 watts, which is more power than you can get out of a standard 120 volt outlet. Your typical Joe Average AC outlet in a home is rated for 15 amps, which is 1800 watts (power is voltage times current, or 120 volts x 15 amps = 1800 watts). If the espresso machine uses more power than that, you’ll have to get a dedicated 240 circuit run for it. I googled a few espresso machines, and found ones that drew anywhere from 750 to 1200 watts. YEMMV (your espresso machine may vary).
But if the OP wants to use a 240-V appliance on a 120-V line, he or she must use a step-up converter that converts 120-V current to 240-V, and can handle the power needed. Possibly, he or she will need a plug adaptor.
And if the appliance is frequency-sensitive, you need more-expensive equipment that basically converts the incoming AC to sone intermediate form, like DC or torque, then converts that to new AC at the new frequency.
:: looks at madmonk28’s link ::
Okay, that is both a step-up and step-down converter. Badly-described, though.
yogakitty, can you give us the model number of the machine? Maybe we can google up a few specs.
It should do just fine on a 240 volt circuit with 3 wires, hot, the other hot, and ground. You only need the neutral if the device has 120V components. In the past code allowed the same wire to be used for neutral and ground, but now requires 4 wires for things with a 120 volt component.
Oh, if you have much electrical experience, running a new 240 volt circuit isn’t a big deal.
The coffeemaker doesn’t have an outlet, it has a jack. Uruguayan jacks are the very rare L type, three circular spokes in a line; adapters for those can be a pain to find but may be easier to find while still in Uruguay than in the US. If you can’t find an adapter, get the jack changed. A transformer should be relatively easy to find.
The easiest way to determine whether an appliance is approved by whichever organism ought’a do that (in this case UL) is by looking at the manual or the stickers on the appliance itself. Some of mine have so many codes (ISO, DIN, CE, UL…) it’s a veritable alphabet soup.
Terminology check, Nava? By “jack” do you mean “socket”, with receptacles instead of pins, on the coffeemaker itself? That sounds rather dangerous, because the supply plug that fits into such a socket would have live pins. I’m surprised that would be allowed. I hope I’m just misunderstanding you.
The thing on the wall with holes and electrical contacts inside the holes, that supplies electricity, is an “outlet”, “socket”, “receptacle”, or “female connector” (really). “Jack” is also used for a female connector, but not usually for wall outlets. The thing with pins, often found on the end of a cord, is a “plug” or “male connector”.
A plug adaptor has a socket on one side and a plug on the other, of different types. It enables a plug of one type to connect to a socket of another type.
I think there are three main possibilities, assuming the coffeemaker can operate on both 50Hz and 60 Hz without problem:[ul][li]The coffemaker can operate on 120V as well as 240V. Either there’s a switch, or it auto-adapts. In this case, all you need is a plug-adaptor to change the Uruguayan plug to a US plug.[/li]
[li]The coffemaker operates on 240V only, and you connect a 120-to-240-V step-up transformer to your 120-V North American outlet. The 240-V outlet on the transformer may or may not be a Urugayan outlet; if not, you need a plug adaptor to accept the coffeemaker’s Uruguayan plug, and allow it to plug into whatever socket the transfoprmer has. The trasnformer that madmonk28 linked appears to have a combination socket on the 240-V side that looks like it can accept at least UK and mainland European (French/German) plugs. Bear in mind that the 120-V side will carry twice the current of the 240-V side to deliver the same power ot the appliance. You may run into limitations of the 120-V circuit feeding your transformer. So if your coffeemaker draws 2 A at 240 V, the transformer will draw 4 A at 120 V. [/li]
[li]The coffeemaker operates on 240-V only, and you provide a 240-V outlet in your house to supply it. This is the most expensive, but safest, 240-V option. A 15-A North American 240-V outlet will have the NEMA 6-15 outlet. You then need to find a plug adaptor between that and the coffeemaker’s Uruguayan plug. Or you can replace the Uruguayan plug with a North American NEMA 6-15 plug.[/ul][/li]
The various North American connectors. NEMA 5-15 is the common 15-A 120-V household plug and socket. NEMA 6-15 is the rare 240-V version. The NEMA 14 series are the ones used for electric dryers and stoves.
Edit: Electrical plugs and sockets around the world. The Uruguayan one seems to be the same as one of the Italian ones.
I used to install commercial espresso machines from time to time and they would usually come with directions to this effect. These machines were identical to the versions sold in Europe-- sometimes they even came with the Euro plug still attached.