Hi there,
In my circuit the standard is 5V power supply.But there is a problem that when i used 5V as standard then when the load is connected the voltage is droped to 3.78V.Can I use the higher power supply to offset this?

 

You need to examine the requirements of the load. How much current at 5v does it require? Then match the power supply with the load. Get a power supply that delivers about 3v more than what is required. In this case use a power supply that is rated at 8 or 9v at the maximum current required.

To help even further, you can use a low drop-out regulator.

Edit: I assume that there is already a 5v regulator on board.

 

Just make sure you don't use the power supply with the higher voltage on a lighter load specified also for 5V. The power supply's voltage drop will be less with a lighter load, possibly damaging the load.

What you want to do works fine with a constant load.