How design a adapter with adjustable output from 5V to 30V

Do you mean, the output is adjustable with a knob?
What do you mean the power is 100W-300W? At 5V max load is 20A, and at 30V max load is 10A?

I mean the output voltage is adjustable from 5V to 30V.
The max power of the system is 300W.
It may appear in 20V with load of 15A.
Could it be achieved?

So it can be loaded at 5V / 60A? Sounds like a difficult design.

What is the end application?

What about set the max load to 10A?
That means the voltage can be adjust from 5V to 30V, and the max load is 10A.
It also can be described as 5V-10A ~ 30V-10A.
Does it can be achieved?
Could you please give me some suggestion?

I thought about the case of 300W, 5V ~ 30V (5V/60A, to 30V/10A).

You can do this using a HiperPLC (LLC) PSU with output = 32V / 10A. Then you use a 2 or 3 phase synchronous buck regulator with adjustable output voltage. A synchronous buck will have high efficiency, and if it has 3 phases the ripple currents will be manageable.

If you limit the design to 5V ~ 30V / 10A, you can probably do it by designing the LLC as follows:

nominal frequency at 30V / 10A = 66 kHz
series resonant frequency ~= 80 kHz
design it with a low parallel Q (i.e. high series inductance, low resonating capacitance)
design it with a low parallel to series inductance ratio (k ratio) - set it close to 2.

Such an LLC design won't be super high efficiency, but it can regulate over a wide range of output voltage if the max output current is fixed. Be careful also to design the PFC capable of running at close to 150 kHz (when output votlage is 5V) - use a very high quality PFC boost diode.

Thanks for your help. But I still don't know how to design the transformer and how to change the frequency.
Do you mean I have to use the '30V/10A' perameter when design the transformer?
And how to set the series resonant frequency? Use an adjustable resistance?
I need your help.

Thanks for your help. But I still don't know how to design the transformer and how to change the frequency.
Do you mean I have to use the '30V/10A' perameter when design the transformer?
And how to set the series resonant frequency? Use an adjustable resistance?
I need your help.

Thanks for your help. But I still don't know how to design the transformer and how to change the frequency.
Do you mean I have to use the '30V/10A' perameter when design the transformer?
And how to set the series resonant frequency? Use an adjustable resistance?
I need your help.

HiperPLC is our product for PFC + LLC power supplies:
http://www.powerint.com/en/products/hiper-family/hiperplc
Study the datasheet, appnote, and RD board report.

When you want to design a PFC+LLC PSU, download PI Expert.
http://www.powerint.com/en/design-support/pi-expert-design-software

In there is a program called PIXls. PIXls resembles Excel. When you run it, select "HiperPLC".