They weren't all equal in power, but since I read up on this a couple decades ago now I can't remember the details.
Do you mean percussion muskets or percussion RIFLE muskets? Because we didn't go straight from smoothbore flintlock muskets to percussion-lock, rifled ones. The first percussion muskets were more or less the old flintlocks retrofitted for percussion. I seem to remember that during the Civil War's early days, some of these were still in use, and that they were 69 caliber, firing either a round ball or "buck and ball--" a particularly nasty short range loading, in which the paper cartridge holding powder and projectile had one full-sized ball and several buckshot.
Anyway, if my memory is correct and they were .69 caliber, that was a tradition going back to the Revolution. The French used .69s, and gave us a lot of their muskets, so that sort of became the standard here for a while. The British musket, the famous Brown Bess, was a .75, and would therefore have been more powerful.
During the US Civil War, the two main rifled muskets used were the Springfield and the Enfield. The Springfield was a .58 caliber, firing a hollow-based slug universally but incorrectly known as a "minnie," after a certain French Army Captain Minie' , who invented a similar slug some years earlier. The Enfield was the British-manufactured equivalent. The South bought lots of them, and the North did too, partly because they needed them and partly to keep them away from the Rebs. The Enfield was a .577 caliber. In practice the difference in caliber wasn't great enough to prompt anybody to produce .58 and .577 ammunition both, although supposedly the Enfield was a bit harder to load (with the standard .58 minnie) when fouled, due to its slightly smaller bore.
There were numerous other muskets produced, usually copies of the Springfield or Enfield designs, by Colt and Remington and just about everyone else and his cousin, but they all used the same ammuniton and would have been equal in power.
The "Zouave Rifle" you can still buy as a replica is a copy of a Remington design that was produced, purchased, but apparently never used in combat. The Zouave is also a .58, but it was a rifle, not a rifled musket. That meant that its barrel was thicker and stronger, able to handle more gunpowder than the rifled muskets could. So it would have been more powerful, if it had been used.
During the opening days of the Civil War, guns were in such short supply that purchasing agents north and south were over in Europe snapping up whatever junk guns might happen to be sitting around. Some of them were earlier British rifled muskets, of a larger caliber (I think .75). The British tried these but found them too powerful for the soldiers to shoot well, so they studied the problem and ended up switching to .577. There were also some French, Dutch, and Prussian rifled muskets which if I remember correctly were up to .80 caliber. A lot of these guns had been converted from smoothbore and so kept their original larger caliber. They would have been powerful enough, but of course the fact that they were sitting around unused, ready for anybody desperate enough to buy them, speaks for itself.