So I bought an rcx 2.0 and have some power functions extension cables that can also convert between PF and 9v. If I would connect PF to an rcx would it work?

Yes, you should be able to run PF motors off the RCX using the PF extension cables. 

One note: the servo motor or IR receivers won't work since the adapter cable only connects to the motor power lines.

5 hours ago, AI toothbrush said:

So I bought an rcx 2.0

As I see some nice interest here: Whenever possible, go for the RCX1.0. Not the 1.5, not the 2.0. What happened is that they just(!) reduced the electronic piece count on the 1.5 and 2.0 bricks as hardware improvement (for them). As far as I can tell - I run these bricks since 1998.

The 1.0 brick has this "DC in socket" ... you can feed it with anything between 9 and 15 V DC or AC. Which means you can run them off a wall wart - for ever. When your creation is designed to function autonomously and without power cable, just unplug it after programming and testing - it then goes to battery operation without glitch. And vice versa.

The 1.5 and 2.0 sets provided also improved firmwares. Which all run flawlessly on the 1.0 bricks as well. There is absolutely no difference. I have had them all - but gave away the 1.5 and 2.0 bricks to folks wanted to have them - for free of course. The 2.0 firmware is available out there.

Best
Thorsten

5 hours ago, dr_spock said:

Yes, you should be able to run PF motors off the RCX using the PF extension cables. 

Confirmed, you really can. You may want to be careful hooking up the PF L and XL motors, as the H-bridge drivers in the RCX bricks can't handle such a load for a long time. You will notice power drop-outs. The PF M motors work really well on the RCX, even under serious load.

Best
Thorsten

10 hours ago, Tcm0 said:

One note: the servo motor or IR receivers won't work since the adapter cable only connects to the motor power lines.

Yeah the PF system has an extra ground and 9v pin on the connectors. The servo motor and ir reciever uses them.