I need advice for power cords

What do you think about upgrading the power cables for the MC75's?
I know they are vintage but would really like to improve the whole system sound quality.  I'd like to improve everything without buying new amps. So what are your opinions and how could it be done.

Read above. CHANGE them. The PS on Mac make them a lot less prone to bad cable. That is the reason they sound good with that dinky PC. Upgrade it, you might get a pleasant surprise. First thing on the list after a newbie arrives here. Listen, listen, listen, change the PC. Then listen. Hee Hee you'll like it..Not to expensive, great upgrade..

Regards

Agree with "Tantejuut". You may also want to consider a power line conditioner.

Humble advice from my limited experience:
1) Don't assume that the same power chord (brand, price point, level, etc...) will work equally well on all your components. Experiment with each one individually.
2) Using different cables on different pieces of equipment can create excellent overall synergy in a system. The effects of different cables can be additive. 
3) Luna Cables make a very organic sounding inexpensive power cable (orange level) that you might like and that will fit your budget and might have good synergy with your equipment.
4) 20 amp dedicated power lines, using 8 or 10 gauge wire, with independent ground... an even more important move that good power cables.
5) I wouldn't spend my budget equally on all components. I'd look at $500-$1K cables and see if one of them really lights up the system when applied to a single component. Then I would supplement with slightly improved placeholders for other components. 
6) Which component is most important is very system dependent. I never had better results from a power cable than one that was put on a pre-amplifier. On another system it was the DAC that was most affected. I've actually found that power amps have been the easiest to improve (or settle into a good zone) with less expensive cables. YMMV

Dude, these are the basics. 1.  You need sufficient gauge. 2. Good quality termination (ie strong set-screw contact).  3 Decent materials.  Copper or silver (don't get distracted by 'nines' or other snake oil).  4.  They really should be flexible.  There is truly no excuse for for the inflexible cables. 

I had great luck with Anticables.  The change was immediate and obvious.  Start with source, DAC, or pre.  If you aren't happy with them send them back for full, no questions refund.