The ACA had a "chargemaster" rule that required hospitals to post a list of standard charges for treatments, but this doesn't include charges for office visits or elective procedures.

More importantly though, these standard fees do not include any negotiated rates between insurance providers and hospitals, making it effectively impossible to comparison shop. A hospital's chargemaster price for procedure X might be $10,000, but might be only $2,000 for a particular insurance provider due to negotiation.

That's the difference between the ACA rule and this EO; the EO forces hospitals to post the real prices for each insurance provider.