By June 17, 2023, if you buy Kenya Power tokens worth ksh. 500, you would get about 17 to 25 units
NOTE that tokens vary depending on your usage. If you consume a lot power then you will get less units. For instance, if you use more than 100 units per month for 3 consecutive months then your rates will be lowered (you will receive fewer units as you are considered a high-power user).
UPDATE: KPLC has revised its power cost. With ksh. 500, you will now get between 17 to 25 units (we have updated this answer to reflect the changes).