Can a UPS be too powerful?
There is no reason the UPS will not work if the input voltage is correct to your country and the output is the correct voltage. The UPS will provide the needed current for the attached devices.
Be sure you have the correct outlets as some higher output units may use a different plug than others. Some may have a standard 15A outlet while others a 20 or 30A (often a twist lock)
Based on your update the Dell should work fine. If you need additional info, a call to the local Dell office or their online Chat will help you as well.
Post the model number for a specific answer. The only problems I can forsee is that the output voltage could be incorrect as mentioned by Dave M., the input circuit might not support enough amperage as mentioned by soandos, or the actual input plug might be of a standard for which you don't have a socket.
Some high-end datacenter UPS units output 208v instead of the standard US mains voltage of 120. If this is the case you can't run your normal equipment on it unless it's designed for 208v. Also the input amperage is specified in the manual. It might require a 20, or 30 amp circuit from the breaker box which may not be what you have in the wall.
Also as mentioned - the twist lock type of plug (probably a NEMA L5-20 or 30) requires a special outlet. Good luck!
UPS current specification represents the maximum current the UPS can give, and is directly proportional to its rated power, if voltage is constant.
If your connected equipment's total power (or current) exceeds this value, your UPS device's protection will trip, or you will damage it. That's why it's always better to take a device with higher nominal power.
However, if you are comparing two completely different models, of a different price range, things may be slightly more complicated with newer server power supplies. For example, 6th generation of HP Proliant servers completely refuse to operate with lower end UPSs, because their voltage waveforms (when operating on battery) produce too much THD. For these servers, a higher end online UPS or double-conversion is needed to continue running during blackouts.
That's why it's important to know exact models of both UPSs. If new UPS is the same model as the previous one, but with a higher rating, then it should only behave better with the same load.