Generator Voltage

As you claim that you have to replace at 400V, the question of which is better does not arise, Mildred.

See that little knob over there? Turn it a smidge to the left.

Maybe. It depends on a lot of things you seem to not know or at least will not freely tell us. A 5% difference in voltage might be on the tolerance edge for some loads so any momentary over-voltage spike might now be too much. An autotransformer with multiple taps could be used to step this down a little bit but depending on your actual unknown equipment this can easily not be needed.

This may come as a silly question, why not buy the correct generator? If you have equipment failures any warranty you have may become null and void.

Actually, this is not a "new" buy, but it was from other site.

Look at the nameplates on the loaded equipment. Are they actually 380 volts? If so the 400 will be within the tolerance for electrical equipment, and the actual voltage by the time you get from the generator to the actual equipment under load will have some voltage drop anyway. I don't see a problem. I assume the generator is an extremely small one, or else it would have an adjustment for voltage output level of about + or - 10%.

Give complete details of the generator. Like power,(KVA), speed, exciter reserve available etc. Generating lower voltage at rated speed may saturate magnetic circuit, for the same load, load current would be higher. If you reduce the speed for lower voltage to maintain the saturation, generator cooling may get affected.So unless completed details are given, no guidance can be provided. Best is ask generator manufacturer

Electrical appliances have a range of voltages they work with, if you were using 380V, the source can range from 380 to 415V your new generator is good enough provided the KVA rating is the same as the old one, if the the new one has less KVA, it could be overloaded

Any voltage can be specified for any system, but most use the voltages that are readily available from an outside source.

As for adjusting the voltage, if you have selected a replacement unit, contact the manufacturer or refer to the manual that should accompany the replacement, it may have the info you need, and if not, the manufacturer certainly should have the info.

"Existing generator" is a very vague term.

As such,expect very vague answers.

To give a better answer,provide better information, such as KVA of the generator,frequency of the output,etc.

A copy of the data plate would be helpful.

Also a description of the loads applied would be beneficial,whether inductive(motors) resistive(heaters),Switch mode power supplies,(UPS,computers,etc.)

We are all willing to help, but shooting in the dark is not likely to hit the bulls eye.