Update power cord

I have a Rotel RB 991 power amp driving a pair of Vandersteen 2 ce speakers. t has a captured power cord now would spending a few bucks to have an IEC power outlet installed and upgrading to a reasonable cost power cord make a difference. I would like to smooth out the top end a bit.
I would certainly give the Cerious Technology CT GE pcs or the Core Power Technology pcs a try. both are superb and 'reasonable' .
This is what I would do first before adding a Chassis IEC socket to your amp (unless you're able to do yourself). Go buy a Furutech FI-15ME AC plug. Install on your fixed cord and I think you will find the results very satisfactory. I've done this to int. amps/CDP's and was amazed how much better things sounded. Very good product along w/the FI-15E IEC connector. Made a wonderful improvement on my Arcam 10 int. amp
I am a believer of upgraded power cords after listening with my own ears but in your case the cost may not be worth it. I would spend the money on a better amp. I think you will notice more of an improvement with a better amp and then trying a better power cord in the future.
I'm also believer, but would not spend for aftermarket power cord. For me the magnitude of improvement isn't enough justified for money spent. $0 stock power cord will still have much better ROI.

an easy tweak-replace the wall duplex with a generic hospital grade unit and hear the difference- YMMV