Can i plug a 115v power bar to 110v - 240v extension?

Most power bars do not convert 250VAC down to 125VAC.
Will your laptop survive if it is fed a voltage twice as high as it needs? Most do not.

 

That would be the safest option. There's a chance the insulation of a 110V rated power bar could break down on a ~ 240V supply.

 

And they almost never provide any indication they have died, leaving you unprotected against power line surges.

Not that you should rely on a power bar or outlet strip to do that in the first place. Instead, use a small battery-operated UPS (Uninterruptible Power Supply) that floats the battery on rectified incoming power and then drives a power inverter from the battery power, thus isolating the output from the vagaries of "dirty" power line input. Make sure the UPS specs say it provides surge and sag protection, even if the back-up time is measured in minutes instead of hours or days.

The key to stopping surges and sags is the battery-operated inverter between the power line and your sensitive equipment. Don't trust a two-dollar, designed-to-fail, MOV (Metal Oxide Varistor) device for this purpose. It's like lightning arresters for antennas: use them, but disconnect and ground the antenna when it's not in use.