Guten Tag Swiss, und Wilkommen!
The 208 and 240V ratings are not the same. Some appliances, such as baseboard heaters, may be dual-rated for use on either system. For some other devices, e.g. motors, the difference is large enough that it could be a problem. I think that our friends in the U.S. sometimes use small buck/boost transformers where a 240V device needs to run on 208V or vice versa.
The 208V rating is the nominal phase-to-phase voltage of a 120/208 wye system.
Most residential single-phase services in the U.S. are 3-wire, with the center-tap of the transformer secondary grounded and brought into the house as the neutral, giving 120V from either line to neutral and 240V between lines.
240V 3-phase delta arrangements also exist in commercial services.
One peculiarly American system is the "4-wire delta" arrangement. It starts as a basic 240V delta service, but you then add a ground to the center-point of one transformer winding and bring it in as a neutral. This provides 120V for small loads between two of the phases and neutral, while still leaving 240V between any two phases. The third phase ends up at 208V to ground.
As far as the practical aspect of wiring your power supplies is concerned, for a single-phase load of 2.5kW you are well within the rating of a 15A 240V receptacle/plug combination (the first image in Sven's post above).
Just remember that because the 240V American supply has both legs "hot", if you have switching, fusing, or circuit-breaker protection on the input, then you should make these devices double-pole.
By the way, the official NEMA designation of the 240V 15A plug is type 6-15. They're available from Leviton, Hubbell, or any of the other main U.S. manufacturers.
[This message has been edited by pauluk (edited 05-06-2003).]